OSAC 2020‐S‐0004

Standard for Interpreting,

Comparing and Reporting DNA

Test Results Associated with

Failed Controls and

Contamination Events

Human Forensic Biology Subcommittee

Biology Scientific Area Committee (SAC)

Organization of Scientific Area Committees (OSAC) for Forensic Science

   
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OSAC Proposed Standard

OSAC 2020‐S‐0004

Standard for Interpreting, Comparing

and Reporting DNA Test Results

Associated with Failed Controls and

Contamination Events

Prepared by  

Human Forensic Biology Subcommittee

Version: 2.1

December 2023

Disclaimer:

This OSAC Proposed Standard was written by the Human Forensic Biology Subcommittee/Biology

Scientific Area Committee of the Organization of Scientific Area Committees (OSAC) for Forensic

Science following a process that includes an open comment period. This Proposed Standard will

be submitted to a standards developing organization and is subject to change.   

There may be references in an OSAC Proposed Standard to other publications under

development by OSAC. The information in the Proposed Standard, and underlying concepts and

methodologies, may be used by the forensic‐science community before the completion of such

companion publications.  

Any identification of commercial equipment, instruments, or materials in the Proposed Standard

is not a recommendation or endorsement by the U.S. Government and does not imply that the

equipment, instruments, or materials are necessarily the best available for the purpose.

To be placed on the OSAC Registry, certain types of standards first must be reviewed by a

Scientific and Technical Review Panel (STRP). The STRP process is vital to OSAC’s mission of

generating and recognizing scientifically sound standards for producing and interpreting forensic
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science results. The STRP shall provide critical and knowledgeable reviews of draft standards or

of proposed revisions of standards previously published by standards developing organizations

(SDOs) to ensure that the published methods that practitioners employ are scientifically valid,

and the resulting claims are trustworthy.

The STRP panel will consist of an independent and diverse panel, including subject matter

experts, human factors scientists, quality assurance personnel, and legal experts, which will be

tasked with evaluating the proposed standard based on a comprehensive list of science‐based

criteria.  

For more information about this important process, please visit our website at:  

https://www.nist.gov/topics/organization‐scientific‐area‐committees‐forensic‐

science/scientific‐technical‐review‐panels  

Version

No.

Issue Date Section Reason

2.0 June 1, 2021  ‐‐  Added to the OSAC Registry and publicly announced.

2.1 December 27, 2023 All Format and font updates only. No content changes made.
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Foreword

Controls are routinely incorporated during DNA testing of forensic and reference samples in

forensic DNA testing laboratories. If all controls generate the expected results, there is a high

level of confidence in the profile data from the associated sample set. A control may fail for

various reasons. In addition, the profile data may indicate a handling error or the presence of

contaminating DNA. Retesting the forensic sample prior to the step in which the problem was

identified may be performed; however, there are circumstances where this may not be feasible

or necessary. Reasons for not conducting retesting include, but are not limited to, the sample

was consumed during the initial analysis, additional testing would exhaust the remaining portion

of the sample or DNA extract eliminating the possibility of future testing, or the associated

profile(s) would not be suitable for comparison even if the controls produced the expected

results.

There are scenarios where it may be possible to interpret, compare, and report data with some

level of confidence, even if the data are associated with the failure of a control or a contamination

event (of a sample or control). Evaluation and reporting of the possibly compromised data may

provide critical and valid information to support the investigation of a criminal case, for example

excluding a person of interest.  To the extent determination of contamination may be influenced

by judgmental bias, persons making that determination should be shielded from irrelevant

information.

It is intended that this standard be used in conjunction with the laboratory’s documented quality

assurance program. This would ensure that proper evaluations, root cause analyses, risk

assessments, and corrective actions, when necessary, have been performed and appropriately

documented for each instance of a failed control or contamination event that occurs in the

laboratory. It is also intended that the laboratory perform the requirementsin thisstandard using

documented protocols for data interpretation, comparison and reporting with appropriate

accompanying validation and protocol verification studies along with the strong reliance on other

available standards for forensic DNA testing (e.g., FBI Quality Assurance Standards for DNA

Testing Laboratories, ANSI/ASB Standards 18, 20, 40, 136 and 139 and OSAC 2020‐N‐0007, Best

Practices Recommendations for the Management and Use of Quality Assurance DNA Elimination

Databases in Forensic DNA Analysis; see Bibliography). This document is not intended to support

the reporting of data associated with failed controls or contamination events without the

associated prerequisite for thorough evaluation of the possible cause and impact of the events

on the data obtained.  

The draft of this standard was developed by the Biological Data Interpretation and Reporting

Subcommittee of the Organization of Scientific Area Committees for Forensic Science.  

Keywords: contamination, failed control, reporting DNA results, DNA interpretation
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Table of Contents

1 Scope .....................................................................................................................................6

2 Normative References........................................................................................................... 6

3 Terms and Definitions............................................................................................................ 6

4 Requirements ........................................................................................................................ 8

Annex A (informative) Supplememtal Information – Foundational Principles............................10

Annex B (informative) Supplemental Information ‐ Examples....................................................13

Annex C (informative) Bibliography ............................................................................................15
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Standard for Interpreting, Comparing and Reporting DNA test Results Associated with Failed

Controls and Contamination Events

1 Scope

This standard provides requirements for the interpretation, comparison, and reporting of DNA

data associated with control failures or contamination where re‐testing is not performed. DNA

data associated with a failed control or a contamination event may still be scientifically valid and

may be relevant to an investigation.  

2 Normative References

There are no normative reference documents. Annex C, Bibliography, contains informative

references.

3 Terms and Definitions

For purposes of this document, the following definitions apply.

3.1

comparison  

The process of examining two or more DNA data sets to assess the degree of similarity or

difference.

3.2

contamination

Exogenous DNA or other biological material in a DNA sample, PCR reaction, or item of evidence;

the exogenous DNA or biological material could be present before the sample is collected or

introduced during collection or testing of the sample.

3.3

failed control

A positive control (3.7) or negative control (3.6) that produces an unexpected result.

3.4

forensic sample

A biological sample originating from and associated with evidence from a crime scene. A sample

associated with evidence from a crime scene may include a sample that has been carried away

from the crime scene.    
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3.5  

interpretation  

The process of evaluating DNA data for purposes including, but not limited to, defining

assumptions related to mixtures and single source profiles, distinguishing between alleles and

artifacts, assessing the possibility of degradation, inhibition, and stochastic effects, and

determining whether the data are suitable for comparison.

3.6

negative control

An analytical control that consists of the reagents used in various stages of testing without the

introduction of sample; no results are expected from a negative control. For DNA testing,

negative controls include extraction blanks/reagent blanks and amplification blanks. A negative

control in DNA testing is used to detect contamination introduced into the assay during the

testing process via reagents, disposables or handling errors (which may impact the results

observed from samples tested at the same time).

3.7

positive control

An analytical control sample that is used to determine if a test performed properly. This control

consists of the test reagents and a known sample that will provide an expected positive response

with the test. For DNA testing, positive controls may include, extraction positive controls and

positive amplification controls.

3.8

reference sample   

Biological material obtained from a known individual and collected forthe purpose of comparison

to evidentiary samples.  

3.9

suitable for interpretation

Data deemed appropriate for interpretation (3.5) based on developmental validation studies, the

laboratory’s internal validation studies, and the laboratory’s documented and verified

interpretation protocol.  

3.10  

unsuitable for comparison  

Data that cannot be used for comparisons for reasons including, but not limited to, poor or

limited data quality, mixture complexity, or a failure to meet quality assurance requirements.

This decision is based on developmental validation studies, the laboratory’s internal validation

studies, and the laboratory’s documented and verified interpretation and comparison protocol.  
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4 Requirements

4.1 The laboratory protocol shall define what constitutes:

4.1.1 Contamination in a negative control

4.1.2 Contamination in a positive control

4.1.3 Contamination in forensic or reference sample DNA test results

4.1.4 A failed positive control

4.1.5 A failed negative control

4.2   The laboratory shall perform and document the assessment of the integrity of the

associated DNA test results to determine the impact of the failed control or contamination.  The

assessment shall be based on scientifically valid principles in DNA analysis and include a

determination of the possible cause and effect of the failed control or contamination, and an

assessment of the risks associated with moving forward with data interpretation vs. those

associated with re‐testing.

4.2.1 If the DNA test results are determined to be suitable for interpretation within the

constraints of the laboratory's internal validation studies and documented interpretation and

comparison protocols and the laboratory does not retest, the laboratory shall perform and report

the interpretation and comparison(s) with applicable statistical analysis.  

4.2.2 If the DNA test results are determined to be compromised to the extent of being

unsuitable for interpretation and retesting is not conducted, the results shall be reported as not

suitable for interpretation according to laboratory policy.

NOTE If the DNA test results are determined to be compromised to the extent of being unsuitable

for interpretation and retesting is conducted, it may be necessary to report results,

interpretations, and comparisons from both the original and second tests.    

4.3 When reporting interpretations and comparisons impacted by a failed control or

contamination event, the report shall identify the associated DNA test results and describe the

nature of the event.

4.4 The laboratory shall have a written protocol for the release of identifying information for

the source of the contamination.

4.5 The case record for each sample associated with a failed control or contamination event

must include documentation of the following for the affected sample(s), as applicable:
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4.5.1 The forensic sample, reference, or control DNA test result that failed or was contaminated.

4.5.2 The likely or known source of contamination.

NOTE The source may be identified by name, employment position or other descriptor as

permitted by law and agency policies.

4.5.3 The likely or known cause of the failed control or contamination.

4.5.4 The impact of the failed control or contaminant on the integrity of the DNA test results.

4.5.5 The determination of whether an affected DNA test result is suitable, or unsuitable, for

interpretation.  
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Annex A

(informative)

Supplemental Information – Historical Principles

When polymerase chain reaction (PCR) testing wasintroduced into crime laboratoriesin the early

1990s, many of the initial issues encountered by researchers using the highly sensitive PCR testing

methods had been recognized.  As a result, standard procedures for preventing contamination

along with quality control and assurance measures were established in forensic DNA testing

laboratories. Even with these critical measures in place, occasional problems occur during DNA

testing. Forensic DNA testing and databasing laboratories typically have a number of processes

in place for monitoring and evaluating the integrity of the DNA testing results obtained from

samples received and processed by the laboratory. When the laboratory identifies instances

where the DNA test results may be compromised, the laboratory followsrequired proceduresfor

establishing the likely cause of the event and for assessing its impact on the data obtained. This

impact assessment step is critical in that the DNA test results may still be valid and further

interpretation may provide valuable information, such as exculpatory evidence.

When performing PCR testing, forensic DNA testing laboratories are required to have a positive

amplification control associated with each set of DNA extracts amplified together[3]. This control

monitors the DNA testing process performed through all steps commencing at the amplification

step. Some laboratories require an additional positive control to be associated with the DNA

extraction batch that then follows the samples through the entire DNA testing process. At the

end of testing, DNA test results from the positive controls(s) should be consistent with the

expected reference single source profile(s). The presence of the correct DNA test results in the

positive control indicates the testing process(es) monitored by the control(s) performed

correctly.

There are several possible causes for a positive control failure (as defined by the laboratory),

including a technical issue (e.g., problem with an instrument or reagent that precludes the test

from working correctly). Similar issues may have occurred with the associated samples. When it

is not possible to use the results due to a concern of accuracy, then retesting starting from a point

before the instrument or reagent issue is necessary to generate test results that can be reliably

interpreted, compared and reported. If retesting is not possible and the integrity of the DNA test

results cannot be confirmed, the results may be reported as “insufficient for comparison” or

“inconclusive” due to the control failure.

In some cases, the positive control failure may be determined to be specific to only that sample,

with the other DNA test results processed with the controlseemingly unaffected. This may occur,

for example, if DNA or reagents were inadvertently not added to the control but added correctly

for the other DNA extracts. In this case, it may be possible to verify that the other results

associated with the failed control can be interpreted, compared and reported after fulfilling the

requirements of this standard without retesting all of the samples involved.
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In addition, when performing PCR testing, forensic DNA testing laboratories are required to have

two negative controls associated with each set of DNA samples tested [3]. One negative control,

typically referred to as a reagent blank or extraction blank control, is started with each set or

batch of samples extracted together; the second negative control is the negative amplification

control started at the amplification step for each set of samples undergoing amplification

together. These two negative controls are processed throughout each step of the DNA test

alongside the associated samples. These two controls consist of all reagents, solutions,

consumable materials, etc. used during the DNA testing process, and it is expected that the

negative controls meet the laboratory’s definition for suitable performance when evaluated at

the end of the testing. When contamination is identified, the laboratory is responsible for

evaluating the likely biological source of the contamination and assessing when and how the

event most likely occurred.

In some situations, the contaminating DNA is only detected in a negative control with no

apparent presence in or effect on any of the other samples tested. This single contamination

event may be due to any number of reasons where DNA could be introduced only into a single

sample, for example, its presence in or on a consumable material used in the laboratory during

testing (e.g., pipette tip, tube). In other situations, the contaminating DNA may be detected in

the profilesfrom othersamplestested along with the control(s) but be present atsuch a low level

that it has minimal to no impact on the quality of the DNA test results obtained from the tested

sample (e.g., DNA profile from a high‐quality single source or two‐person mixed DNA profile with

a very low level minor component consistent with the profile in the negative control and possibly

other samples). In these cases, the DNA test results may be reasonably determined, interpreted

and used for comparison according to established laboratory protocols in accordance with the

requirements listed in this document.

DNA contamination may also be present in one or more of the forensic or reference samples.

Many laboratories have internal DNA databases comprised of DNA data from laboratory or other

personnel who may routinely come into contact with samples or are present in the environment

where forensic samples are handled or processed (e.g., law enforcement, evidence technicians,

crime scene investigators, maintenance staff). These DNA databases may be used as a screening

mechanism for the detection of possible DNA contamination events (also see Best Practice

Recommendations for the Management and Use of Quality Assurance DNA Elimination

Databases in Forensic DNA Analysis). Similarly, some laboratories compare the data obtained

within certain test batches to screen for possible contamination events that may have occurred

between DNA extracts processed concomitantly. During these evaluations, the source of the

contaminating DNA may be identified. In this situation, it may be possible to evaluate the DNA

test results even in the presence of contaminating DNA from a known individual, similar to the

interpretation steps used to evaluate mixed DNA test results when a known contributor to a DNA

mixture is assumed. The use of an assumed contributor in the interpretation and comparison of

the data should be reported according to the laboratory’s protocol and best practice

recommendations for reporting evaluations performed using assumed contributors.  
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Additional standards and best practice recommendations are referenced in the Bibliography that

may be used in conjunction with this standard and provide additional useful information.

   
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Annex B

(informative)

Supplemental Information – Examples

The following examples describe different scenarios where samples are associated with a failed

control or contamination event with some possible outcomes responsive to the requirements of

this standard:

1. No results were obtained for the amplification positive control. The associated forensic

samples provided partial or full profiles that corresponded logically to their respective

quantitation results and, where predictable, the expected results (e.g., single source DNA

profile from a presumed blood stain or sperm fraction; non‐sperm/epithelial fraction

results consistent with complainant; duplicate amplifications of a DNA extract).

Amplification results consistent with expectations confirm the PCR amplification was

successful and that the allele calling by the software was appropriate. Based on the

laboratory’s root cause investigation, it was determined that the analyst most likely did

not add the known DNA to the amplification positive control sample, and the associated

profiles were interpreted and used for comparison purposes. The issue and resolution

were documented in the case record and the results were reported per the laboratory

protocol since the results were not directly impacted by the failed control.

2. The DNA profile of a member of the laboratory was detected as a minor component of a

two‐person mixture profile detected from a forensic sample. The laboratory staff member

wasthe individual who performed the latent print examination on the sample prior to the

DNA testing. The DNA profile was interpreted and used for comparison under the

assumption that the laboratory staff member was one of the contributors to the mixture.

Since the interpretation was directly impacted, the contamination event was described in

the report.

3. A low‐level DNA profile was detected in the extraction reagent blank that was consistent

with the low level DNA profile detected from the forensic sample. The forensic sample

and DNA extract were consumed during testing. Investigation could not determine the

cause of the contamination event (e.g., whether cross contamination occurred or

whether the reagents themselves were contaminated).    The results for the forensic

sample were reported as not suitable for comparison purposes. Since the contamination

event directly impacted the interpretation of the profile from the forensic sample, the

contamination event was described in the report.  

4. The DNA profile from the forensic sample associated with a failed positive control

demonstrated the presence of a mixture of at least six individuals. The assessment of the

impact of the failed positive control determined that the interpretation of the forensic

sample profile was not affected since the laboratory’s protocol does not permit the

interpretation of mixtures of greater than four individuals. No retesting was performed;
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the forensic sample profile was reported as not suitable for comparison purposes due to

the high number of contributors.

5. The DNA profile of the working DNA analyst was detected in the epithelial cell fraction of

a sexual assault kit sample and there was no indication of contamination of the sperm

fraction. Because the remaining contributor profile in the epithelial cell fraction was

consistent with the complainant, retesting was not performed. Results from both the

epithelial cell fraction and sperm cell fraction were interpreted, used for comparison and

reported. Since the contamination event directly impacted the interpretation of the

forensic sample profile, the contamination event was described in the report.

6. The DNA profile of the technician who performed amplification set up was detected in

the negative amplification control.  A review of the associated samples shows that they

were not impacted by the contamination and no retesting was performed. The issue and

resolution were documented in the case record and the results were reported per the

laboratory protocol since the results were not directly impacted by the contamination.

7. The DNA profiles from an amplification plate show a low‐level contaminant throughout,

indicating that there may have been contamination of the amplification master mix.

Because of the way the contaminant presents, the associated forensic sample profiles

were determined to be unsuitable for comparison. The DNA amplified includes the

consumed extract of a single swab (also consumed) from the neckline of a shirt. The

neckline of the shirt is resampled by taking and consuming a second swab, and an

interpretable profile is obtained. The laboratory report should address both the first and

second sampling of the neckline of the shirt.

   
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Annex C

(informative)

Bibliography

1] Forensic Science Regulator. Forensic Science Providers: Codes of Practice and Conduct.

2014. Available at https://www.gov.uk/government/collections/forensic‐science‐ providers‐

codes‐of‐practice‐and‐conduct.

2] SWGDAM Contamination Prevention and Detection Guidelines for Forensic DNA

Laboratories. Available at www.swgdam.org.

3] Federal Bureau of Investigation. Quality Assurance Standards for Forensic DNA Testing

Laboratories. Current version available at www.swgdam.org.

4] ISO/IEC 17025 Testing and Calibration Laboratories. Current version available at

https://www.iso.org/ISO‐IEC‐17025‐testing‐and‐calibration‐laboratories.html.

ANSI/ASB and/or OSAC Standards and Best Practices Applicable to this Standard

5] OSAC 2020‐N‐0007, Best Practice Recommendations for the Management and Use of Quality

Assurance DNA Elimination Databases in Forensic DNA Analysis. Current version available at

https://www.nist.gov/osac/osac‐registry (accessed May 2021).

6] ANSI/ASB Standard 136, Forensic Laboratory Standards for Prevention, Monitoring, and

Mitigation of DNA Contamination, 1st. Ed. (currently in review at ASB; has been out for public

comments).

7] ANSI/ASB Standard 018, Validation Standardsfor Probabilistic Genotyping Systems. 2020. 1st.

Ed.

http://www.asbstandardsboard.org/wp‐content/uploads/2020/07/018_Std_e1.pdf

(accessed October 2020).

8] ANSI/ASB Standard 020, Standard for Validation Studies of DNA Mixtures, and Development

and Verification of a Laboratory’s Mixture Interpretation Protocol. 2018. 1st. Ed.

https://asb.aafs.org/wp‐content/uploads/2018/09/020_Std_e1.pdf

(accessed December 2020).

9] ANSI/ASB Standard 040, Standard for Forensic DNA Interpretation and Comparison Protocols.

2019. 1st. Ed.

http://www.asbstandardsboard.org/wp‐ 

content/uploads/2019/10/Std_040_e1.pdf (accessed December 2020).
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10] ANSI/ASB Standard 139, Reporting DNA Conclusions. (currently in review at ASB; has been

out for public comments).