Guidance for Industry 

and FDA Staff 

 
Review Criteria for Assessment of 
C-Reactive Protein (CRP), High 
Sensitivity C-Reactive Protein 
(hsCRP) and Cardiac C-Reactive 
Protein (cCRP) Assays 
 
 
 
 
Document issued on: September 22, 2005 

 
 
This document supersedes:
   
In Vitro Diagnostic C-Reactive Protein Immunological Test System 

Issued on July 20, 1998
  
 
For questions regarding this document contact James V. Callaghan 240-276-0443 or by email 
james.callaghan@fda.hhs.gov   
 
 
  U.S. Department of Health and Human Services 
Food and Drug Administration 
Center for Devices and Radiological Health
   Office of In Vitro Diagnostic Device Evaluation and Safety 
Division of Chemistry and Toxicology Devices 
 
 
  Contains Nonbinding Recommendations 
 
Preface
  
 
Public Comment  
Written comments and suggestions may be submitted at any time for Agency consideration to 
the Division of Dockets Management, Food and Drug Administration, 5630 Fishers Lane, 
Room 1061, (HFA-305), Rockville, MD, 20852.  When submitting comments, please refer to 
the exact title of this guidance document.  Comments may not be acted upon by the Agency 
until the document is next revised or updated.   
 
Additional Copies 
  Additional copies are available from the Internet at: 
http://www.fda.gov/cdrh/oivd/guidance/1246.pdf , or to receive this document by fax, call 
the CDRH Facts-On-Demand system at 800-899-0381 or 301-827-0111 from a touch-tone 
telephone. Press 1 to enter the system.  At the second voice prompt, press 1 to order a 
document.  Enter the document number (1246) followed by the pound sign (#).  Follow the 
remaining voice prompts to complete your request.   
 
  2 
    Contains Nonbinding Recommendations 
 
 
 
Table of Contents 

1.   INTRODUCTION .......................................................................................................................................4
  
2.   BACKGROUND ..........................................................................................................................................5
  
3.   CONTENT AND FORMAT OF AN ABBREVIATED 510(K) SUBMISSION .....................................6
  
4.   SCOPE..........................................................................................................................................................7 
 
5.   TYPES OF CRP ASSAYS ..........................................................................................................................8 
 
6.     RISKS TO HEALTH..................................................................................................10 

7.   DEVICE DESCRIPTION .........................................................................................................................11 
 
8.   ANALYTICAL PERFORMANCE CHARACTERISTICS ..................................................................11 
 
9.   METHOD COMPARISON ......................................................................................................................15 
 
10.   CLINICAL INFORMATION ..................................................................................................................17 
 
11.   LABELING................................................................................................................................................18 
 
12.   REFERENCES ..........................................................................................................................................21 
 
 
 
 
  3 
    Contains Nonbinding Recommendations 
 
Guidance for Industry and FDA Staff 

 
Review Criteria for Assessment of C-

Reactive Protein (CRP), High Sensitivity 

C-Reactive Protein (hsCRP) and Cardiac 

C-Reactive Protein (cCRP) Assays 

 
This guidance represents the Food and Drug Administration's (FDA's) current thinking 
on this topic. It does not create or confer any rights for or on any person and does not 
operate to bind FDA or the public.  You can use an alternative approach if the approach 
satisfies the requirements of the applicable statutes and regulations. If you want to discuss 
an alternative approach, contact the FDA staff responsible for implementing this 
guidance. If you cannot identify the appropriate FDA staff, call the appropriate number 
listed on the title page of this guidance.  
1.   Introduction  
This guidance is intended to provide device manufacturers and FDA staff with updated 
recommendations concerning 510(k) submissions for various types of assays for C-Reactive 
Protein (CRP). The document is a revision of Guidance for Industry: In Vitro Diagnostic C-
 
Reactive Protein Immunological Test System, issued on July 20, 1998.  It is updated to 
address issues associated with the development of hsCRP (high sensitivity CRP) and cCRP 
(cardiac CRP) assays.  These types of CRP assays have significantly lower limits of 
detection, and functional sensitivities that may be used to support new clinical uses of CRP 
  
quantitation.  This document now includes discussion of how you should support indications 
for use claims of cCRP for the evaluation of patients with coronary disease and coronary 
syndromes in premarket submissions, including how you should assess different ranges of 
measurement, based on indications for use.  Additionally, we provide recommendations for 
limitations of CRP test interpretation based on the non-specific nature of CRP elevations in 
 
blood. 
 
FDA's guidance documents, including this guidance, do not establish legally enforceable 
responsibilities. Instead, guidances describe the Agency's current thinking on a topic and 
should be viewed only as recommendations, unless specific regulatory or statutory 
requirements are cited.  The use of the word should in Agency guidances means that 
something is suggested or recommended, but not required.  
 
   
The Least Burdensome Approach 
The issues identified in this guidance document represent those that we believe should be 
addressed before your device can be marketed.  In developing the  guidance, we carefully 
considered the relevant statutory criteria for Agency decision-making.  We also considered 
the burden that may be incurred in your attempt to follow the guidance and address the issues 
we have identified. We believe that we have considered the least burdensome approach to 
resolving the issues presented in the guidance document.  If, however, you believe that there 
is a less burdensome way to address the issues, you should follow the procedures outlined in 
the A Suggested Approach to Resolving Least Burdensome Issues document.  It is 
available on our Center web page at:  
  
http://www.fda.gov/cdrh/modact/leastburdensome.html. 
2.   Background 
A manufacturer who intends to market a CRP test system should conform to the general 
controls of the Federal Food, Drug and Cosmetic Act (the Act), including the premarket 
notification requirements described in 21 CFR 807 Subpart E, and obtain a substantial 
equivalence determination from FDA prior to marketing the device.  
 
This guidance document identifies the classification regulations and product codes for 
various types of CRP tests. (Refer to Section 4  Scope.)  In addition, other sections of this 
guidance document list the risks to health identified by FDA from the various CRP tests and 
describe measures that, if followed by manufacturers and combined with the general controls, 
will generally address the risks associated with these kinds of CRP tests and lead to a timely 
[510(k)] review and clearance. This document supplements other FDA documents regarding 
the specific content requirements of a premarket notification submission.  You should also 
refer to 21 CFR 807.87 and other FDA documents on this topic, such as the 510(k) Manual -
Premarket Notification: 510(k) - Regulatory Requirements for Medical Devices, 
http://www.fda.gov/cdrh/manual/510kprt1.html  
 
As explained in The New 510(k) Paradigm - Alternate Approaches to Demonstrating 
Substantial Equivalence in Premarket Notifications; Final Guidance1, a manufacturer 
may submit a Traditional 510(k) or has the option of submitting either an Abbreviated 510(k) 
or a Special 510(k), when appropriate.  FDA believes an Abbreviated 510(k) provides the 
least burdensome means of demonstrating substantial equivalence for a new device, 
particularly once FDA has issued a guidance document.  Manufacturers considering 
modifications to their own cleared devices may lessen the regulatory burden by submitting a 
Special 510(k). 
                                                           
1  http://www.fda.gov/cdrh/ode/parad510.html  
  5 
     
3. 	  Content and Format of an Abbreviated 510(k) 
Submission 
An Abbreviated 510(k) submission must include the required elements identified in 21 CFR 
807.87, including the proposed labeling for the device sufficient to describe the device, its 
intended use, and the directions for its use. In an Abbreviated 510(k), FDA may consider the 
contents of a summary report to be appropriate supporting data within the meaning of 21 
CFR 807.87(f) or (g); therefore, we recommend that you include a summary report.  The 
report should describe how this guidance document was used during the device development 
and testing and should describe the methods or tests used and a summary of the test data, 
description of the acceptance criteria applied to address the risks identified in this document, 
and any additional risks specific to your device.  This section suggests information to fulfill 
some of the requirements of 807.87 as well as some other items that we recommend you 
generally include in an Abbreviated 510(k). 
 
Coversheet 
The coversheet should prominently identify the submission as an Abbreviated 510(k) and 
cite the title of this guidance document. 
 
Proposed labeling 
Proposed labeling should be sufficient to describe the device, its intended use, and the 
directions for its use. (Refer to Section 11 for specific information that should be 
included in the labeling for devices of the types covered by this guidance document.) 
 
Summary report 
We recommend that the summary report contain the following: 
 
	   A description of the device and its intended use.  We recommend that the 
description include a complete discussion of the performance specifications and, 
when appropriate, detailed, labeled drawings of the device.  You should also 
submit an "indications for use" enclosure.2    
 
	   A description of device design and its requirements.  
 
	   Identification of the Risk Analysis method(s) used to assess the risk profile in 
general as well as the specific devices design and the results of this analysis.  
(Refer to Section 5 for the risks to health generally associated with the use of this 
device that FDA has identified.) 
 
	   A discussion of the device characteristics that address the risks identified in this 
guidance document, as well as any additional risks identified in your risk analysis.  
 
                                                           
2 Refer to  http://www.fda.gov/cdrh/ode/indicate.html for the recommended format. 
 
  6 
     
	   A description of the test method(s) you used to address each performance aspect 
identified in Sections 8-9 (and 10, if appropriate) of this guidance document.  If 
you follow a suggested test method, you may cite the method rather than 
describing it.  If you modify a suggested test method, you may cite the method but 
should provide sufficient information to explain the nature of and reason for the 
modification.  For each test, you may either (1) present the data resulting from the 
test in clear form, such as a table, or (2) describe the acceptance criteria that you 
apply to your test results.3  (See also 21 CFR 820.30, Subpart C - Design Controls 
for the Quality System Regulation.) 
 
	   If you choose to rely on a recognized standard for any part of the device design or 
testing, you may include either: (1) a statement that testing will be conducted and 
meet specified acceptance criteria before the product is marketed, or (2) a 
declaration of conformity to the standard.4  Because a declaration of conformity is 
based on results from testing, we believe you cannot properly submit a declaration 
of conformity until you have completed the testing the standard describes.   
 
If it is not clear how you have addressed the risks identified by FDA or additional risks 
identified through your risk analysis, we may request additional information about aspects of 
the devices performance characteristics.  We may also request additional information if we 
need it to assess the adequacy of your acceptance criteria.  (Under 21 CFR 807.87(l), we may 
request any additional information that is necessary to reach a determination regarding  
substantial equivalence.) 
 
As an alternative to submitting an Abbreviated 510(k), you can submit a Traditional 510(k) 
that provides all of the information and data required under 21 CFR 807.87 and described in 
this guidance.  A Traditional 510(k) should include your data, as well as methods, acceptance 
criteria, and conclusions. Manufacturers considering modifications to their own cleared 
devices should consider submitting Special 510(k)s.  
4.   Scope 
The scope of this document is limited to the following devices as described in 21 CFR 
866.5270, C-reactive protein immunological test system.   
 
The product codes are: 
 
DCH - System, Test, C-Reactive Protein, Rhodamine 
DCK - C-Reactive Protein, Antigen, Antiserum  
DCN - System, Test, C-Reactive Protein  
                                                           
3 If FDA makes a substantial equivalence determination based on acceptance criteria, the 

subject device should be tested and shown to meet these acceptance criteria before being 

introduced into interstate commerce.  
 
4 See Required Elements for a Declaration of Conformity to a Recognized Standard
  
(Screening Checklist for All Premarket Notification [510(K)] Submissions), 

http://www.fda.gov/cdrh/ode/reqrecstand.html. 

  7 
     
NQD - Cardiac C-Reactive Protein, Antigen, Antiserum  
 
 (a) Identification. A C-reactive protein immunological test system is a device that consists of 
the reagents used to measure by immunochemical techniques the C-reactive protein in serum  
and other body fluids. Measurement of C-reactive protein aids in evaluation of the amount of 
injury to body tissues. 
(b) Classification. Class II (performance standards). 
 
The devices addressed in this guidance document are for prescription use. 
5.   Types of CRP  Assays  
The following types of CRP assays have been cleared: 
 
   Conventional C-Reactive Protein (CRP) 
   High sensitivity CRP (hsCRP) 
   Cardiac C-Reactive Protein (cCRP) 
 
Conventional CRP  
Conventional CRP assays include qualitative, semi-quantitative and quantitative assays, with 
indications for use for evaluation of infection, tissue injury, and inflammatory disorders.   
These assays provide information for the diagnosis, therapy, and monitoring of inflammatory 
diseases. CRP is one of the cytokine-induced "acute-phase" proteins [1] whose blood levels 
rise during a general, unspecific response to infections and non-infectious inflammatory 
processes [2].   For conventional CRP assays, test values are typically considered to be 
clinically significant at levels above 10 mg/L.  In apparently healthy persons blood CRP 
levels are below 5 mg/L, while in various conditions this threshold is often exceeded within 
four to eight hours after an acute inflammatory event, with CRP values reaching 
approximately 20 to 500 mg/L. [3] 
  
CRP is a more sensitive and more reliable indicator of acute inflammatory processes than the 
erythrocyte sedimentation rate (ESR) and leukocyte count. Blood CRP levels rise more 
rapidly than ESR, and after the disease has subsided CRP values rapidly fall and reach the 
reference interval often days before ESR has returned to normal. [4, 5]  
 
High sensitivity CRP (hsCRP) 
High sensitivity CRP assays have a range of measurement that extends below the 
measurement range typical of most conventional CRP assays.  This lower range of 
measurement may expand the indications for use to include the evaluation of conditions 
thought to be associated with inflammation in otherwise healthy individuals. Increases in 
CRP values are non-specific and should not be interpreted without a complete clinical 
evaluation. Indications for hsCRP assays are general and not associated with specific 
diseases or risks for disease. 
  
  8 
     
Cardiac C-Reactive Protein (cCRP) 
Cardiac CRP assays are indicated for use as an aid in the identification and stratification of 
individuals at risk for future cardiovascular disease.  When used in conjunction with 
traditional clinical laboratory evaluation of acute coronary syndromes, cCRP may be 
useful as an independent marker of prognosis for recurrent events in patients with stable 
coronary disease or acute coronary syndrome.  Cardiac CRP assays, like hsCRP assays, 
have measurement ranges that extend below the measurement range typical of most 
conventional CRP assays. The difference between hsCRP and cCRP is not the analyte itself, 
but is due to the additional performance validation to support the expanded intended use in 
the evaluation of coronary disease discussed below.  For cCRP, the validity of the indications 
related to cardiovascular disease should be demonstrated in clinical studies.  You may use 
literature based on a predicate device to support a cCRP claim for your device if you present 
bridging studies, showing comparability of values across devices, to support transfer of  
clinical findings to the new cCRP device.  Bridging studies should demonstrate 
comparability of devices in terms of method comparison study results, precision, and 
interference.  In addition, to enable comparison of cCRP assay results to each other, cCRP 
assays should be standardized to IFCC/BCR/CAP CRM 470, a certified reference material 
for the acute-phase reactants  [6].  Manufacturers of cCRP assays should always emphasize in 
the device labeling that increases in CRP values are non-specific and should not be 
interpreted without a complete clinical evaluation. 
 
The table below outlines similarities and differences between these 3 types of assays, in 
terms of intended use and performance features that you should demonstrate in a 510(k). 
 
  Conventional  hsCRP  cCRP 
CRP 
Intended use  For evaluation of  For evaluation of  For aid in identification 
  infection, tissue  conditions thought to  and stratification of 
injury, and  be associated with  individuals at risk for 
inflammatory  inflammation, in  cardiovascular disease. 
disorders.  otherwise healthy  When used in 
  individuals.  conjunction with 
Provides  traditional clinical  
information for the  laboratory evaluation 
diagnosis, therapy,  of acute coronary 
and monitoring of  syndromes, cCRP may 
inflammatory  be useful as an 
disorders.  independent marker of 
prognosis for recurrent 
events, in patients with 
stable coronary disease 
or acute coronary 
syndrome.  
  9 
     
Typical clinical  Cutoff:   Cutoff:   1.0 mg/L  Cutoff:  1.0 mg/L 
cutoff  approximately 10 
concentrations  mg/L. 
Apparently healthy 
individuals:  5 
mg/L 
Acute range: 20-
500 mg/L 
Appropriate   5mg/L to upper  < 1.0 mg/L to   10.0  < 1.0 mg/L to   10.0 
assay measuring  range of the assay  mg/L  mg/L 
range 
 
Analytical  Describe  Determine limit of   Determine limit of  
sensitivity  performance at the  quantitation (functional  quantitation (functional 
information    low end of claimed  sensitivity)  sensitivity) 
assay range 
Clinical or   Comparison of new  Comparison of new  Comparison of new 
method  device to a  device to a predicate  device to a predicate 
comparison   predicate device  device  device whose clinical 
information    utility and cutoff has 
been demonstrated 
or 
Presentation of results 
from literature 
describing clinical 
utility of the new 
device 
or 
Clinical studies for the 
new device. 
Standardization  Describe assay  Describe assay  Describe assay 
of new device   standardization or  standardization or  standardization. Assay 
traceability  traceability. Assay  should be standardized 
should at a minimum  to IFCC/BCR/CAP 
be traceable to  CRM 470 
IFCC/BCR/CAP CRM 
470 
6.   Risks to Health 
Failure of a CRP assay to perform as indicated may lead to improper patient management.  A 
falsely low or falsely high measurement could contribute to improper risk assessment or 
improper differentiation of tissue injury and inflammatory processes, from non-inflammatory 
processes. A false result for a cCRP assay could result in assignment of inappropriate risk 
stratification for individuals thought to be at risk for cardiac events.  In addition, an error in 
  10 
     
interpretation of results, such as use of assay results to adjust a treatment regimen without 
consideration of other clinical factors, may also lead to improper patient management.   
 
In the table below, FDA has identified the risks to health generally associated with the use of 
CRP tests addressed in this document.  The measures recommended to mitigate these 
identified risks are given in this guidance document, as shown in the table below.  We  
recommend that you conduct a risk analysis, prior to submitting your premarket notification, 
to identify any other risks specific to your device.  The premarket notification should 
describe the risk analysis method.  If you elect to use an alternative approach to address a 
particular risk identified in this document, or have identified risks additional to those in this 
document, you should provide sufficient detail to support the approach you have used to 
address that risk. 
 
 
Identified risk  Recommended mitigation measures 
Improper patient management:   
Due to failure of the device to perform as  Sections 8-9 (and 10, if appropriate) 
indicated 
 
Due to misdiagnosis based on incorrect  Section 11 
use 
7.   Device Description 
You should identify your device by regulation and product code in your 510(k). 
 
For any CRP test, you should fully describe the principle method of the assay in the 510(k).  

For new technologies or methods, you should also provide details on how this new method 

for CRP relates to predicate CRP assays, cleared with the same indications for use as your 

assay. 

8.   Analytical Performance Characteristics  
General Study Recommendations  
 
Whenever possible, we recommend that you include patient samples or sample pools, derived 
from the intended use population (i.e., apparently healthy individuals suspected to be at risk 
of the specific inflammatory associated condition or disease) for the various analytical 
protocols described below. If sufficient samples at the low end of the assay range cannot be 
obtained from such samples, then we recommend supplementing with patient samples or 
sample pools derived from healthy individuals, at low risk of inflammatory conditions or 
disease. 
 
  11 
     
Although spiked samples can be used to supplement the analytical studies, FDA cautions 
against using spiked samples as the only matrix in the evaluations, because spiked samples 
may not provide an accurate assessment of the performance characteristics.  FDA 
recommends that you do not use hemolysates in the analytical studies because these 
specimens may not test the effects of all preparatory steps on test performance. 
 
So that acceptance criteria or results can be best interpreted during the review, we 
recommend that you provide appropriate specifics concerning protocols.  These specifics are 
also necessary to aid users in interpreting information in your labeling. For example, when 
referring to CLSI (Clinical Laboratory Standards Institute)/NCCLS protocols or guidelines, 
we recommend that you indicate which specific aspects of the protocols or guidelines you 
followed, and describe any modifications. 
 
Generally, we recommend that performance be assessed in the testing environment where the 
device will ultimately be used (i.e., central laboratory or point of care), by the types of  
individuals who will use the test in clinical practice (e.g., trained technologists, nurses).  We  
recommend that you initially analyze data separately to evaluate any inter-site variation and 
include results of the analysis in the 510(k) summary report.  You may be able to pool 
method comparison results from the individual sites in the package insert if you demonstrate 
that there are no significant differences in the results among sites.  You may contact OIVD 
before initiating a clinical study.  
 
The intended use of your device should be compatible with the performance characteristics 
of the assay; for example, assays that do not meet high sensitivity performance criteria 
should not claim use for evaluation or stratification of patients for diseases associated with 
inflammation.  Additionally, claims for cardiac risk stratification should be supported with 
clinical data, whether from new studies, peer-reviewed literature sources using the same  
device for which clearance is sought, or literature together with device-specific bridging 
studies. 
 
Specific Performance Characteristics  
Precision of Quantitative C-Reactive Protein Assays  
For quantitative assays, we recommend that you characterize within-run, and total precision 
using patient samples or sample pools.  We recommend that you follow guidelines provided 
in Evaluation of Precision Performance of Quantitative Measurement Methods; Approved 
Guideline Second edition (2004) CLSI (Clinical Laboratory Standards Institute)/NCCLS, 
EP5-A2. That document includes guidelines for experimental design, computations, and a 
format for stating performance claims.  
You should evaluate precision at relevant CRP concentrations, including near medical 
decision points, and concentrations near the limits of reportable range.  We recommend that 
for hsCRP and cCRP assays, one level should be at the American Heart Association/Centers 
for Disease Control and Prevention (AHA/CDC)  clinical cutoff for low risk category (1.0 
mg/L) [7] and should have a C.V. 10%, another should be at a mid-point of the assay range 
and the third should be at or near the upper limit of the assay.  We recommend that you 
describe the following items in your 510(k): 
  12 
     
   sample types (e.g., serum, plasma, or whole blood) and preparation, or origin 
   sites at which the protocol was run 
   number of days, runs, and observations 
   target concentrations 
   mean and standard deviations for within-run and total precision  
We recommend that you describe which factors (e.g., instrument calibration, reagent lots, 
operators) were held constant, and which were varied during the evaluation, as well as the 
computational methods, if they are different from that described in CLSI/NCCLS EP5-A2. 
Precision studies for a point of care setting should be conducted at three sites by intended 
users such as nurses, technicians, doctors, etc. 
Precision of Qualitative/Semi Quantitative CRP Assays  
For qualitative assays, we recommend you follow User Protocol for Evaluation of 
Qualitative Test Performance; Approved Guideline (2002), CLSI/NCCLS, EP12-A, to 
establish an estimate of precision.  You should test negative and positive samples at 
concentrations within 20% of the cutoff, since evaluation of low-negative or high-positive 
samples would not challenge the assay. We recommend that you test 20 replicates of each 
sample and calculate percent agreement for the negative samples and also the positive 
samples.   
In your 510(k), you should describe your study design, including sample types, study sites, 
and factors varied (e.g., days, operators). 
Interference  
We recommend that you characterize the effects of potential interferents on assay 
performance.  Examples of experimental designs, including guidelines for selecting 
interferents for testing, are described in Interference Testing in Clinical Chemistry; 
Approved Guideline (2002)  CLSI/NCCLS, EP7-A.  
 
Typically, interference studies involve adding the potential interferent to a serum sample and 
determining any bias in the recovery of CRP relative to a control sample (to which no 
interferent has been added). 
 
We recommend that you describe the following concerning your study design: 
 
   types and levels of interferents tested  
   a description of the samples tested (e.g., matrix, preparation, origin)   
   concentrations of CRP in the sample 
   definition or method for computing interference (including replicates tested) 
  13 
     
We recommend that you identify any observed trends in bias (i.e., negative or positive) and 
indicate the range of observed recoveries in the presence of the particular interferent.  This 
approach is more informative than listing average recoveries alone. 
 
We recommend that you state the criteria on which non-interference is determined.  For 
example: Inaccuracies due to bilirubin are less than x% at CRP concentrations of 1.0 mg/L.   
 
You may not need to perform additional interference testing with interferents identified in 
literature or by other sources. However, you should identify these interferents in your 
instructions for use. 
Sensitivity  
For CRP assays claiming high sensitivity (hsCRP or cCRP), you should calculate and report 
the limit of quantitation (LOQ) of the assay, (sometimes also referred to as functional 
sensitivity).  We use this term to mean the lowest concentration at which assay bias and 
precision are within acceptance criteria, under your stated experimental conditions.  
Acceptance criteria for precision should be %CV  20%. The LOQ should be significantly 
below the clinical cut-off of the assay (1.0 mg/L in the case of cardiovascular risk assessment 
with cCRP tests). In determining the LOQ, we recommend that you follow Protocols for 
determination of Limits of Detection and Limits of Quantitation; Approved Guideline (2004), 
CLSI/NCCLS, EP-17A. 
 
You may also wish to report the limit of blank, also discussed in further detail in 
CLSI/NCCLS, EP-17A . This is often determined as the highest measurement results likely 
to be observed for a blank sample.  Typically, manufacturers determine two or more standard 
deviations (SD) above the mean of the zero standard or calibrator, by repeated measurements 
of one or more blank samples, such as the zero calibrator.  
 
The determination of the limit of the blank for conventional CRP assays may be clinically 
irrelevant, if that limit is considerably below the clinical cutoff.  In such cases, you may 
choose not to state this value in the label.  However, you should describe assay performance 
(e.g. linearity, precision) at the low end of the claimed assay range or clinical cutoff. 
 
In the description of your sensitivity evaluation, we recommend that you describe your study 
design, calculations, and definition of your measures of sensitivity.  You should also provide 
results, acceptance criteria, and clarification of how measurements below the level of 
sensitivity are reported to the user. 
Linearity   
For quantitative or semi-quantitative tests, we recommend that you characterize the linear 
range of the assay by evaluating samples whose concentration levels are known relative to 
each other. Evaluation of the Linearity of Quantitative Measurement Procedures, A 
Statistical Approach; Approved Guideline (2003), CLSI/NCCLS, EP6-A describes a protocol 
for sample preparation and value assignment as well as a format for stating performance 
characteristics. 
We recommend that you describe the sample types and preparation, concentrations and 
statistical methods or calculations used (including replicates tested).  When describing 
  14 
     
your acceptance criteria or summary data, we recommend that you include the slope and 
intercept with confidence intervals, the estimated regression line, the range of linearity  
and the degree of deviations (biases) from the estimated line that were observed or that 
are considered acceptable for the various concentration levels.  We recommend that you 
list observed or acceptable values relative to the expected values for each level you 
evaluated. 
Specimen collection and handling conditions  
You should substantiate statements in your labeling about specimen storage and transport by 
assessing whether the device can maintain acceptable performance (e.g., precision) over the 
storage times and temperatures recommended to users. For example, an appropriate study 
may include an analysis of aliquots stored under the conditions of time, temperature, or 
allowed number of freeze/thaw cycles. We recommend that you state your criteria for an 
acceptable range of recoveries under the recommended storage and handling conditions.  
Calibration  
We recommend that you provide the following information about the calibrators in the 
assay kit: 
	   Protocol and acceptance criteria for real-time or accelerated stability studies 
for opened and unopened calibrators. 
	   Protocol and acceptance criteria for value assignment and validation, 
including any specific instrument applications or statistical analyses used. 
	   Identification of traceability to a domestic or international standard reference 
material.  FDA recommends that cCRP assays should be standardized to 
IFCC/BCR/CAP CRM 470 and hsCRP assay should at a minimum be 
traceable this standard. 
	   Protocol and acceptance criteria for the transfer of performance of a primary 
calibrator to a secondary calibrator. 
For information about calibrators marketed separately as class II devices under 
862.1150, see the guidance Abbreviated 510(k) Submissions for In Vitro Diagnostic 
Calibrators,  http://www.fda.gov/cdrh/ode/calibrator.html. 
9.   Method Comparison 
General Recommendations 
You should compare results obtained with your device to those obtained with a predicate 
device with similar indications for use and similar assay range.  Banked (retrospective) 
samples may be appropriate for the studies as long as appropriate information concerning 
sample characterization is available.  
 
You should evaluate patient samples with CRP concentrations distributed across the 
reportable range of the assay. Regardless of whether prospective or retrospectively collected 
  15 
     
samples are used, we recommend that you provide a clear description of how the samples 
were selected, including reasons that samples are excluded. We recommend that you indicate 
whether samples are chosen from patients with specific clinical outcome or risk profiles 
pertinent to indications for either conventional CRP assays or hsCRP or cCRP assays.  
 
We recommend that you follow guidelines provided in Method Comparison and Bias 
Estimation Using Patient Samples; Approved guideline (2002) CLSI/NCCLS, EP9-A2, 
concerning experimental guidelines and statement of performance characteristics. 
Appropriate sample size depends on factors such as precision, interference, range, and other 
performance characteristics of the test.  We recommend that you provide a statistical 
justification to support the study sample size.  
 
Method comparison studies for a point of care setting should be conducted at three sites by 
intended users such as nurses, technicians, doctors, etc.  At least 40 samples at each site 
should be tested with a minimum of 25 percent of the samples having values near the cut-off 
concentration.  You may be able to pool method comparison results from the individual sites 
in the package insert if you demonstrate that there are no significant differences in the results 
among sites.   
 
You may contact OIVD for input on your study plan prior to initiating the studies.  
 
Additional considerations for hsCRP and cCRP method comparison 
evaluations 
 
For cCRP assays, you should compare your new assay directly to a predicate device for 
which clinical studies are available to support clinical utility of the specific device.  Results 
of your study should support transferability between the assays. 
 
In order to fully evaluate the clinically relevant range for accuracy for a hsCRP assay, your 
method comparison to the predicate or reference assay should encompass the entire assay 
range starting from less than 1.0 mg/L.  The rationale for this is that CRP levels less than 1.0 
mg/L are generally considered below the clinical cut-off for hsCRP measurements.  (For this 
reason, we believe the analytical cutoff should also be significantly less than 1.0 mg/L.)  The 
evaluation should extend to 5.0 mg/L or greater, but not more than 10.0 mg/L.  Patient 
samples should be evenly distributed throughout this range.  Your study should demonstrate 
that the assay can accurately measure values between the LOQ and 5.0 mg/L, in order to 
encompass the clinically meaningful stratification values recommended by the AHA/CDC 
[7]. 
 
Considerations for qualitative conventional CRP assays  
 
Qualitative conventional CRP assays are usually  devices with a titration format, e.g., latex 
particle agglutination assays.  These assays are generally not sensitive in the low range of  
measurement, and are not able to differentiate degree of disease state, but are intended to 
evaluate qualitatively for disease versus non-disease states.  The clinical cut-off for 
conventional CRP assays is frequently between 5.0 and 10.0 mg/L. For such tests we 
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recommend that you follow guidelines provided in the document User Protocol for 
Evaluation of Qualitative Test Performance; Approved Guideline (2002), CLSI/NCCLS, 
EP12-A concerning experimental guidelines and statement of performance characteristics.  
 
Presentation of results 
 
We recommend that you conduct a separate analysis of data for each group.  Specifically, for 
hsCRP, it may be appropriate to separately analyze apparently healthy individuals referred 
for risk evaluation for a condition related to inflammation and individuals known to be at risk 
or to have inflammatory disorders. For conventional CRP, you should analyze patients with 
non-inflammatory processes versus inflammatory processes.  When providing the results of 
the method comparison study, we recommend that you include the following information: 
 
	   Quantitative or semi-quantitative tests: plots of results from the new assay (y-axis) versus 
the reference method (x-axis) or predicate, including all of the data points, the estimated 
regression line and the line of identity. Data points should represent individual 
measurements.  If a predicate device is used for comparison, we recommend that you 
employ Deming regression, or another method that accounts for variability in both test 
systems.  You should provide a description of the analytical method used to fit the 
regression line and results of regression analysis, including the slope and intercept with 
their 95% confidence limits, the standard error of the estimate (calculated in the y 
direction), and a coefficient of determination and an estimate of systematic bias at 
medical decision points.  
	   Qualitative tests: a 2 X 2 table showing agreement between the new assay (rows) versus 
the reference method or predicate device (columns), and calculations of the percent 
positive, percent negative, and overall agreement between the methods, including the 
95% confidence intervals or other measure of robustness where appropriate. 
10.   Clinical Information 
Based on the studies described above, you should demonstrate transferability of reference 
intervals, between the new device and a predicate, for which clinical utility has already been 
demonstrated.  We recommend using guidelines in How to Define and Determine Reference 
Intervals in the Clinical Laboratory; Approved Guideline, Second Edition 2000, 
CLSI/NCCLS C28-A2.  Specifically, if the new test system has similar imprecision and 
known interferences, comparable standards and calibrators, and is acceptably comparable in 
absolute values to a predicate device previously cleared for the same indication, then the 
reference interval can generally be transferred, and further clinical studies will generally not 
be needed. 
 
In accordance with the least burdensome provisions, the agency will rely upon well-designed 
bench (and/or animal testing) rather than requiring clinical studies for new devices unless 
there is a specific justification for asking for clinical information to support a determination 
of substantial equivalence. However, we may request clinical studies in the following 
instances: 
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The indications for use are dissimilar from CRP assays of the same type. 
 	 
 
The performance of the new CRP assay does not allow for reference interval transfer 
 	 
previously determined in clinical studies used in support of the indication.   
 
We will consider alternatives to clinical testing when the proposed alternatives are supported 
by an adequate scientific rationale. 
 
Data to support clinical utility can be based on clinical studies you conduct.  You should 
conduct these studies (e.g. method comparison studies, precision studies) in two or more 
external sites, in addition to that of the manufacturer.  Your support for clinical utility can 
also be based on literature, when available, for example, a meta-analysis of information 
derived from the literature using the new device.  If you are conducting a clinical study to 
demonstrate substantial equivalence, refer to Blue Book Memorandum entitled Significant 
Risk and Nonsignificant Risk Medical Device Studies http://www.fda.gov/cdrh/d861.html. 
11.   Labeling 
The premarket notification should include labeling in sufficient detail to satisfy the 
requirements of 21 CFR 807.87(e).  Although final labeling is not required for 510(k) 
clearance, final labeling must also comply with the requirements of 21 CFR 809.10 before a 
medical device is introduced into interstate commerce.  The following suggestions are aimed 
at assisting you in preparing labeling that satisfies the requirements of 21 CFR 807.87(e) and 
21 CFR 809.10. 
 
Directions for use    
You should include clear and concise instructions that delineate the technological 
features of your device and how it is to be used on patients.  Instructions should 
encourage local/institutional training programs designed to familiarize users with the 
features of the device and how to use it in a safe and effective manner.   
 
Intended Use 
As discussed above, the intended use should be compatible with the performance 
characteristics of the assay.  Assays that do not meet high sensitivity performance 
criteria, and are not supported by bridging studies or literature should not claim use 
for evaluating patients for specific diseases associated with inflammation; rather, the 
intended use of such assays should be limited to the general use in the detection and 
evaluation of infection, tissue injury, and inflammatory disorders.   
 
Summary and Explanation 
You should explain that CRP is an acute phase protein and rises non-specifically in 
response to inflammation. You should also clarify that intra-individual variation is a 
major limitation of the assay when the assay is used for directing therapies and 
include recommendations such as the following: 
 
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	   Intra-individual variations of the CRP levels are from 30 to 60%.  Serial 
measurements may be required to estimate true mean of CRP depending on 
the intended use in any specific individual.  
  
If a claim is made for use in coronary disease evaluation, or for the evaluation of 
other inflammatory associated conditions, you should further emphasize the 
non-specific nature of CRP and include clear recommendations that CRP values 
should not be interpreted without a complete clinical evaluation.  Additionally, you 
should recommend follow up-testing of patients with elevated values in order to help 
rule out a recent response to undetected infection or tissue injury.   
 
Principle of the Method 
If you used literature to support clearance of the new device, you should discuss how 
your method is traceable to the method used in the supportive literature, as discussed 
above. For cCRP, methods should be standardized to IFCC/BCR/CAP CRM 470. 
 
Limitations  
You should thoroughly discuss the limitations of the assay.  You should also discuss 
any recommended practice or other expert recommendations concerning the 
limitations of CRP for the intended use. 
 
As an example, an AHA/CDC Scientific Statement, [7] based on investigation of the 
use of hsCRP and cardiovascular disease, made several recommendations for 
limitations on the use of Cardiac C-Reactive Protein (cCRP).   These 
recommendations are highlighted below, and should be included in the labeling of all 
assays seeking cCRP indications for cardiac risk evaluation: 
 
	   Screening the entire adult population is not recommended.     
	   CRP is not a substitute for traditional cardiovascular risk factors. 
	   Acute coronary syndrome management should not depend on CRP measurements. 
	   When being used for risk assessment, patients with persistently unexplained CRP 
levels above 10 mg/L should be evaluated for other non-cardiovascular origins. 
	   Testing for any risk assessment should not be performed while there is indication 
of infection, systemic inflammation, or trauma. 
	   Secondary prevention measures should be based on global risk assessment and 
not depend on CRP. 
	   Serial testing of CRP should not be used to monitor effects of treatment. 
	   The average of CRP results repeated optimally two weeks apart should be used in 
performing risk assessment on metabolically stable patients. 
 
Interpretation of Results 
You should include the following, with your interpretation of results: 
	   Express CRP, hsCRP, and cCRP measurements in mg/L. 
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	   Clarify that results below the lower limit of detection should be reported as less 
than that of the value of the lower limit of detection.  
	   Emphasize the need for detailed clinical evaluation and follow-up testing of 
elevated hsCRP and cCRP results. 
	   Indicate the imprecision at the 99th percentile of the reference population. This 
value should be  10% C.V. 
	   Intra-individual variations of CRP are significant and should be taken into 
account when interpreting values. 
 
Performance Characteristics 
You should summarize all study designs and describe performance characteristics as 
discussed in Sections 8-9 (and 10, if appropriate) of this document.   
 
Precision 
You should describe within-run and total precision, determined at three levels.  As 
discussed in the precision section above, one level should be at the clinical cutoff of 
normal, another should be a mid-point of the assay range from the cutoff and the third 
should be at or near the upper limit of the assay. 
 
Sensitivity 
For high sensitivity assays, you should report functional sensitivity (limit of 
detection), as well as limit of blank.  You may also wish to report sensitivity based on 
the measurements of blank samples (e.g., zero calibrator).  (See the Sensitivity 
section, above.) 
 
Assays with multiple ranges 
It is possible that a CRP assay may offer two ranges of measurement (full range).  In 
these instances, performance of the hsCRP or cCRP range of measurement should be 
characterized and presented independently from the performance of the conventional 
CRP range of measurement. 
 
Method Comparison 
You should present the method comparison results evenly distributed across the assay 
range appropriate for the intended use of your assay.  For example, in cardiovascular 
and peripheral vascular disease risk assessment, the clinically relevant range is from  
values of < 1.0 mg/L to 5.0 mg/L, but not more than 10 mg/L.  You should 
summarize the study design and results of your analyses, including the slope and 
intercept, with 95% confidence intervals, standard error, and coefficient of 
determination.  We recommend that you display the data in a scatter plot.   
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12.   References 
                                                           
1.   Kushner I. The Phenomenon of the Acute Phase Response. Ann NY Acad Sci 1982; 
39:389. 
2. 	  Kind CRH, Pepys MB. The role of C-reactive Protein (CRP) Measurement in Clinical 
Practice. Int Med 1984; 5:112-151. 
3. 	  Kushner I., Rzewnicki DL. The Acute Phase Response: General aspects. Baillieress 
Clinical Rheumatology 1994; 8:513-530. 
4. 	  Dixon JS, Bird HA, Sitton NG. C-reactive protein in the serial assessment of disease 
activity in rheumatoid arthritis. Scand J Rheum 1984;13:39-44. 
5. 	  Gambino R. C-Reactive Protein: An Underutilized Test. Lab Report for Physicians 
1989; 11:41. 
6. 	  Kimberly MM, Vesper HW, Caudill SP, Cooper GR, Rifai N, Dati F, Myers GL. 
Standardization of Immunoassays for Measurement of High-Sensitivity C-reactive 
Protein. Phase I: Evaluation of Secondary Reference Materials. Clinical Chemistry., 
2003; 49(4) 611616 
7. 	  Pearson, T A, .Mensah, G A,.Alexander RW, Anderson JL, Canon RO 3rd, Criqui M, 
Fadl YY, Fortmann SP, Hong Y, Myers GL, Rifai N, Smith SC Jr, Taubert K, Tracy 
RP, Vinicor F, Markers of Inflammation and Cardiovascular Disease: Application to 
Clinical and Public Health Practice: A Statement for Healthcare Professionals From  
the Centers for Disease Control and Prevention and the American Heart Association. 
Circulation., 2003;107:499-511. 
 
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