Developing a Proficiency Testing Plan for your Laboratory 

Author and Presenter: Jeff C. Gust 

Vice President 

Quametec Proficiency Testing Services 

501 W. Van Buren St 

Columbia City, IN 46725 

(260) 244-7450 

gust@quametec-pt.com

Abstract 

Whether responding to new requirements from accreditation bodies, or ensuring that your 

laboratory quality system meets the requirements of ISO 17025, developing a documented plan 

for Proficiency Testing benefits the laboratory. Formal development of a Proficiency Testing Plan 

provides a long term “roadmap” for laboratories to ensure validation of all calibration services that 

they provide, and conveniently summarizes corrective and preventive actions that result from 

participation in proficiency testing. When developing a Proficiency Test Plan, it is important to 

optimize the costs to the laboratory by ensuring that the minimum requirements are met and the 

entire technical scope of the laboratory is covered in the required timeframe. 

This presentation will discuss the proficiency testing requirements from the International 

Laboratory Accreditation Cooperation, through the regional accreditation organizations, to the 

accreditation bodies, and the laboratory itself. Information will be shared on the development of 

the NIST Weights and Measures Division Proficiency Test Policy and Plan that was jointly 

developed by NIST and Quametec Proficiency Testing Services. Examples of Proficiency 

Testing Plans for laboratories will be provided. 

What is a Proficiency Test? 

A proficiency test (PT) is simply, a method that you may use to validate a particular measurement 

process. The artifact’s reference value is not known by the participating laboratory at the time of 

its measurement (test). In a well designed proficiency test, the reference value for the artifact 

should be principally determined by a competent laboratory with appropriate traceability to the 

International System of Units (SI). The reference laboratory should also have demonstrated its 

competency though key comparisons, interlaboratory comparisons, or proficiency tests 

appropriate to validate their measurement capability. It is also preferable that the laboratory has 

had its competency independently assessed through the process of laboratory accreditation. 

Lastly, in order to appropriately validate the measurement capability of the participating 

laboratory, the uncertainty assigned to the artifact by the reference laboratory should be 

sufficiently smaller than the expanded uncertainty reported by the participating laboratory. 

Why does my laboratory need a Proficiency Testing Plan? 

Regardless of the standard that your calibration laboratory’s quality system is based upon, 

proficiency testing is an excellent way to validate one’s measurement processes. Proficiency 

tests can validate the participating laboratory’s measurement method, technical training, 

traceability of standards, and uncertainty budgets. Even though the laboratory has been most 

rigorous in developing the aforementioned laboratory processes, it is important to use proficiency 

testing as an additional way to verify that all aspects of the laboratory measurement system are 

sound. 
For laboratories that must either comply to or be accredited to ISO 17025, this document provides 

specific guidance why proficiency testing is important, and why it is preferable to develop a 

Proficiency Testing Plan. Section 5.9 of ISO 17025, Assuring the quality of test and calibration 

results, states that the laboratory is required to have procedures to monitor the validity of 

calibrations. The laboratory is required to plan and review the monitoring process. This section 

goes on to suggest several ways to accomplish the monitoring, one of which is participation in 

proficiency tests. 

Proficiency Testing and the Accreditation Process 

In order for a calibration laboratory to be accredited to ISO 17025, the accreditation body often 

has specific requirements for participation in proficiency tests. Before discussing specific 

accreditation body proficiency testing requirements, it is helpful to understand why proficiency 

testing is required to be accredited. 

In order for an accreditation body to be eligible to enter into a Mutual Recognition Arrangement 

(MRA) with the International Laboratory Accreditation Cooperation (ILAC) or a regional 

accreditation cooperation such as the Asia Pacific Laboratory Co-operation (APLAC), the 

accreditation body must develop a quality system which meets the criteria for recognition. ILAC 

provides the procedure ILAC P1:2003 “ILAC Mutual Recognition Arrangement Requirements for 

Evaluation of Accreditation Bodies by ILAC Recognized Regional Co-operations” which sets forth 

the requirements for entry into a MRA. 

ILAC P1:2003 specifies in section 5, Criteria for Evaluation, requirements of proficiency testing 

activities that the accreditation body must require of laboratories that they accredit. Section 5.3 

recommends that at a minimum, laboratories successfully participate in at least one proficiency 

test prior to gaining accreditation and one proficiency test relating to each major sub-area of 

major disciplines of a laboratory’s scope of accreditation during a four-year period. 

Regional organizations such as the National Cooperation for Laboratory Accreditation (NACLA) 

and the Asia Pacific Laboratory Accreditation Cooperation (APLAC) further clarified the 

requirements of ILAC P1:2003 within their quality system documents. For example, APLAC 

MR0001 “Procedures for Establishing and Maintaining Mutual Recognition Agreements Between 

Accreditation Bodies” Section 3.3 requires accreditation bodies to specify that accredited 

laboratories participate in a minimum of one proficiency test prior to accreditation and one 

proficiency test for each major sub-area of major disciplines of a laboratory’s scope of 

accreditation at least every four years. 

The following paragraphs summarize the proficiency testing requirements of some of the major 

accreditation bodies in the United States. This is not a complete listing of all accreditation bodies, 

so if your accreditation body is not included in this list, please contact your accreditation body for 

proficiency testing requirements. 

PT Requirements – A2LA 

Some accreditation bodies such as the American Association for Laboratory Accreditation (A2LA) 

have supplemented the ILAC recommendation by requiring laboratories participate in a minimum 

of two proficiency tests per year and cover all major sub-disciplines of the laboratory technical 

scope every four years (Document - A2LA Proficiency Testing Requirements January 1, 2004) in 

addition to the requirement of successfully completing at least one proficiency test prior to 

obtaining accreditation. A2LA also requires that accredited laboratories have a documented plan 

of how they intend to cover their technical scope during the four year period. Details of the 

documented plan requirements will be discussed later. At the time of writing this paper, A2LA 

has not defined “major sub-disciplines” as it relates to calibration laboratories. 
PT Requirements – NVLAP 

The National Voluntary Laboratory Accreditation Program (NVLAP) most recent version of 

Handbook 150 has no specific minimum proficiency testing requirements, but NVLAP has 

published two documents in the 150-2 series (150-2C technical guide for time and frequency 

measurements and 150-2E technical guide for optical radiation measurements) do specify that 1 

proficiency test is to be completed per year per field, where a field is represented within the 

specific document such as 150-2C or 150-2E. At the time of writing this paper, there are no 

formally released publications to cover any fields of calibration other than those mentioned in this 

paragraph. 

PT Requirements – LAB 

Laboratory Accreditation Bureau’s Policy 002 on proficiency testing requires laboratories to have 

satisfactorily completed at least one proficiency test before accreditation will be granted. The 

policy goes on further to state that accredited laboratories must complete a minimum of one 

proficiency test per major field each year for 25% of the major fields of their technical scope, so 

that all major fields of the technical scope is covered in a four year period. The LAB policy goes 

on to further state that laboratories participate in at least two proficiency tests per year. LAB also 

requires the laboratory to submit a proficiency testing schedule to the accreditation body so that 

LAB may monitor compliance to the schedule. LAB defines major fields of calibration in Policy 

002 as Electrical, Mechanical, Dimensional, Pressure, Thermodynamics, Force, and Torque. 

PT Requirements – NIST Weights and Measures Division (WMD) 

The NIST WMD is not a formal accreditation body following ISO Guide 58 and does not enter into 

national or international agreements for acceptance and reciprocity. However, the WMD 

manages the State laboratory program, which is a program that provides training, guidance, and 

technical assistance to State legal metrology laboratories to ensure that measurements made by 

these laboratories are traceable to NIST. In addition, NIST Handbook 143, Program Handbook 

contains the requirements for participation in the measurement assurance program, which are 

based on ISO/IEC 17025. 

NIST WMD and Quametec Proficiency Testing Services has recently developed and published 

(Document number not available at this time) Proficiency Test Policy and Plan to aid State 

weights and measures laboratories in meeting the requirements of NIST Handbook 143. This 

document also requires applicant laboratories to successfully complete at least one proficiency 

test prior to obtaining recognition by WMD. Laboratories that are recognized to NIST Handbook 

143 must complete one proficiency test per year at a minimum and participate in at least one 

proficiency test for each major sub-discipline during a four year period. The NIST WMD 

Proficiency Test Policy and Plan defines Major Disciplines and Major Sub-Areas for NIST WMD. 

Lastly, this document requires proficiency tests to be planned to meet the participation 

requirements. 

Key Elements in Developing a Proficiency Testing Plan 

When developing a Proficiency Testing Plan for your laboratory, the first element to consider is 

the length of the proficiency testing cycle for your laboratory. The laboratory should plan to 

participate in enough proficiency testing activities to cover the technical scope of the laboratory. If 

your laboratory is not accredited, you can select any length of time for the cycle that suits you, but 

if you are applying for accreditation, it is advisable to align your proficiency test plan to the 

requirements of the accreditation body to which you are applying. If you are an accredited 

laboratory, the maximum cycle time that you can select is four years. It is important to note that 

the laboratory may select a smaller period of time for the proficiency testing cycle. A shorter 

cycle may be necessary for laboratories with a small technical scope of accreditation to meet 

additional accreditation body requirements, or may be desirable if the laboratory is interested in a 

more comprehensive quality program. For accredited laboratories, beginning with selecting the 

maximum cycle time of four years minimizes cost to the laboratory while still ensuring compliance 

to applicable requirements. 
The next element to consider is the definition of “Major Discipline” and “Major Sub-Area” as it 

applies to your technical scope of accreditation. Again, if you are not an accredited laboratory, 

you can define these terms yourself. One possible source of guidance for defining these terms 

(which can be used for both laboratories and accreditation bodies) can be found at the Bureau 

International des Pois et Mesures (BIPM) Key Comparison Database (KCDB). This information 

can be located at http://kcdb.bipm.org//. This database (in appendix C, Calibration and 

Measurement Capabilities) defines Major Disciplines and Major-Sub Areas used in the support of 

the Mutual Recognition Arrangement (MRA). If your accreditation body has defined major 

disciplines and major sub-areas, you must align your Proficiency Testing Plan to these definitions. 

If you accreditation body has not defined major disciplines and major sub-areas, please consult 

with your accreditation body for further guidance, preferably in writing. 

Example of Key Comparison Database for Electricity and Magnetism 

For some accreditation bodies, it may not be enough to cover the laboratory technical scope in 

the four year period; the accreditation body may require a minimum number of tests per year be 

completed. For example, A2LA and LAB requires that the laboratories participate in two tests per 

year at a minimum, regardless of the number of major sub-areas contained on a scope of 

accreditation. 

Lastly, some accreditation bodies require that the proficiency test plan must: 

• include information such as an explanation of why proficiency testing may not be 

possible for certain major sub-areas 

• address the laboratory’s process for timely submission of proficiency testing results to 

the accreditation body in the required timeframe 
• complete and implement corrective actions for measurement areas that have received 

unsatisfactory proficiency testing results and submit the information to the accreditation 

body in a timely manner. 

Documenting the Proficiency Test Plan 

Once the laboratory technical scope has been divided into major disciplines and major sub-areas 

and minimum annual proficiency testing requirements are understood, the laboratory may begin 

to schedule proficiency testing activities. The proficiency test may be either from a commercial 

provider, developed internally, or completed through a cooperative effort such as those provided 

by NCSL International, but the proficiency test must meet the applicable requirements of the 

accreditation body, such as the requirement that the proficiency test be designed in accordance 

with ISO Guide 43-1 (1997), Proficiency Testing by Interlaboratory Comparisons – Part 1: 

Development and operation of proficiency testing schemes. 

The scheduling of proficiency tests to be accomplished during the proficiency testing cycle, 

proficiency tests already accomplished, and other previously mentioned elements should be 

contained in a single, easy to use document. There are no formatting requirements for the 

document, so the laboratory may develop a document that meets the requirements of the 

accreditation body (or their own requirements if the laboratory is not accredited). It is also 

permissible for the laboratory to work with consultants or proficiency test providers (some of 

which will develop a Proficiency Testing Plan at no charge and include price discounts to the 

laboratory) in the development of their Proficiency Test Plan. It is important to understand that 

despite whoever develops the Proficiency Testing Plan, it is the ultimate responsibility of the 

laboratory to ensure that the data is correct and the plan is carried out. 

In order to aid the reader, an example of a Proficiency Testing Plan is included in the appendix of 

this document. 

Conclusion

In order to develop a successful PT plan for your laboratory, it is important to understand the 

documented PT requirements from your accreditation body. It is also helpful to review the quality 

system requirements that your accreditation bodies must comply to in order to have a better 

understanding of what drives the PT policies of your accreditation provider. 

A well developed and documented PT schedule will allow better oversight and management of 

PT requirements, spreading tests out over the entire technical scope of the laboratory instead of 

over-concentrating in one particular area. The time and resources associated with proficiency 

testing is generally associated with overhead costs of operating a laboratory, so it is usually 

desirable to minimize these costs. A well constructed PT plan will allow the laboratory to meet 

quality and accreditation requirements and verify the measurement processes associated with the 

laboratory technical scope at a minimum of expense. 

References 

ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories. 

International Organization of Standardization, 12/15/1999. 

ILAC P1:2003, ILAC Mutual Recognition Arrangement: Requirements for Evaluation of 

Accreditation Bodies. International Laboratory Accreditation Cooperation 2003. 

APLAC MR-001, Procedures for Establishing and Maintaining Mutual Recognition Arrangements 

Amongst Accreditation Bodies. Asia Pacific Laboratory Accreditation Cooperation 12/02. 
A2LA Proficiency Testing Requirements for Accredited Testing and Calibration Laboratories. 

American Association for Laboratory Accreditation 10/01/03. 

White, V.R., Alderman D.F., Faison C.D. NIST Handbook 150 (2001 Edition), National Voluntary 

Accreditation Program Procedures and General Requirements. National Institute of Standards 

and Technology 7/01. 

Faison, Douglas C, BrickenKamp, Carroll S. editors. NIST Handbook 150-2C National Voluntary 

Accreditation Program Calibration Laboratories Technical Guide for Time and Frequency 

Measurements. National Institute of Standards and Technology 9/01. 

Faison, Douglas C, BrickenKamp, Carroll S. editors. NIST Handbook 150-2E National Voluntary 

Accreditation Program Calibration Laboratories Technical Guide for Optical Radiation 

Measurements. National Institute of Standards and Technology 8/01 

LAB Policy 002, Proficiency Testing. Laboratory Accreditation Bureau, 01/07/03. 

Gust, Jeff, Harris, Georgia et al. Proficiency Test Policy and Plan. National Institute of Standards 

and Technology, Weights and Measures Division (document not published at time of this paper 

printing). 
Appendix A 

 Example Proficiency Test Plan for LAB Accredited Laboratory 

Proficiency Testing Plan 

XXX Calibration, Inc. 

LAB Certificate ZZZ 

Date Generated: 10/02/2003 

Plan Developed by: Quametec Proficiency Testing Services 

Summary Schedule for Coverage of Scope 

Field Proficiency Test Scheduled Date 

Dimensional QPTS Micrometer #1 03/2003 

Electrical QPTS DC Volt #1 09/2003 

Force QPTS Force #1 03/2006 

Torque QPTS Torque #1 09/2004 

Pressure QPTS Pressure #1 03/2005 

Thermodynamic QPTS Temperature #1 09/2006 

1

Accredited Proficiency Test Planned, but not yet available 

2

No Commercial Tests are available at this time, if no commercial tests are 

available by the date shown, the laboratory will develop a test to satisfy this 

parameter. 

Summary Schedule for Annual Proficiency Test Participation 

Date Proficiency Test Status Any 

Unsatisfactory 

Results? 

(Y/N) 

Date 

Submitted to 

Accreditation 

Body 

03/15/03 QPTS Micrometer #1 Complete No 04/10/03 

09/06/03 QPTS DC Volt #1 Complete No 09/26/03 

03/2004 QPTS Caliper #1 Scheduled 

09/2004 QPTS Torque #1 Scheduled 

03/2005 QPTS Pressure #1 Scheduled 

09/2005 QPTS Resistance #1 Scheduled 

03/2006 QPTS Force #1 Scheduled 

09/2006 QPTS Humidity #1 Scheduled 

Technical Manager:_______________________ 

Date:________________ 
Appendix A 

 Example Proficiency Test Plan for LAB Accredited Laboratory 

Detailed Proficiency Test Schedule 

Field Parameter Proficiency Test Scheduled Date 

Dimensional Gage Blocks 

 Height Gages 

 Indicators 

 Calipers QPTS Caliper #1 03/2004 

 End Standards 

 OD Micrometers QPTS Micrometer #1 03/2003 

 Rules and Scales 

 Cylindrical Gages – Major 

Diameter 

 

 Cylindrical Gages – Minor 

Diameter 

 

 External Thread Gages 

Electrical DC Current - Measure 

 DC Voltage –Measure QPTS DC Volt #1 09/2003 

 Resistance – Measure QPTS Resistance #1 09/2005 

 Electrical RTD Simulation – 

Generate 

 

 Electrical TC Simulation – 

Generate 

 

 AC Voltage – Measure 

 AC Current – Measure 

Force Force - Generate QPTS Force #1 03/2006 

Torque Torque – Generate QPTS Torque #1 09/2004 

Pressure Pressure – Generate Hydraulic 

 Pressure – Generate Pneumatic QPTS Pressure #1 03/2005 

Thermodynamic Relative Humidity QPTS Humidity #1 09/2006 

 Temperature – Generate 

 Pyrometric Indicators 

 TC Probes 

 Temperature Uniformity Survey