2020-S-0004 Standard for Interpreting, 

Comparing and Reporting DNA Test Results Associated with 

Failed Controls and Contamination Events

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

Organization of Scientific Area Committees (OSAC) for Forensic Science
2020-S-0004 Standard for Interpreting, 

Comparing and Reporting DNA Test Results Associated with 

Failed Controls and Contamination Events

Draft OSAC Proposed Standard

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: 1.0

December 2020

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
2020-S-0004 Standard for Interpreting, 

Comparing and Reporting DNA Test Results Associated with 

Failed Controls and Contamination Events

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/scientifictechnical-review-panels
2020-S-0004 Standard for Interpreting, 

Comparing and Reporting DNA Test Results Associated with 

Failed Controls and Contamination Events

1 Foreword

2 Controls are routinely incorporated during DNA testing of forensic and reference 

3 samples in forensic DNA testing laboratories. If all controls generate the expected 

4 results, there is a high level of confidence in the profile data from the associated sample 

5 set. A control may fail for various reasons. In addition, the profile data may indicate a 

6 handling error or the presence of contaminating DNA. Retesting the forensic sample

7 prior to the step in which the problem was identified may be performed; however there 

8 are circumstances where this may not be feasible or necessary. Reasons for not 

9 conducting retesting include, but are not limited to, the sample was consumed during 

10 the initial analysis, additional testing would exhaust the remaining portion of the sample 

11 or DNA extract eliminating the possibility of future testing, or the associated profile(s) 

12 would not be suitable for comparison even if the controls produced the expected results.

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

14 with some level of confidence, even if the data are associated with the failure of a 

15 control or a contamination event (of a sample or control). Evaluation and reporting of 

16 the possibly compromised data may provide critical and valid information to support 

17 the investigation of a criminal case, for example excluding a person of interest. To the 

18 extent determination of contamination may be influenced by judgmental bias, persons 

19 making that determination should be shielded from irrelevant information.

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

21 documented quality assurance program. This would ensure that proper evaluations, 

22 root cause analyses, risk assessments, and corrective actions, when necessary, have 

23 been performed and appropriately documented for each instance of a failed control or 

24 contamination event that occurs in the laboratory. It is also intended that the laboratory 

25 perform the requirements in this standard using documented protocols for data 

26 interpretation, comparison and reporting with appropriate accompanying validation 

27 and protocol verification studies along with the strong reliance on other available 

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

29 Testing Laboratories, ANSI/ASB Standards 18, 20, 40, 136 and 139 and OSAC Best 

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

31 Elimination Databases in Forensic DNA Analysis; see Bibliography). This document is 

32 not intended to support the reporting of data associated with failed controls and/or 

33 contamination events without the associated prerequisite for thorough evaluation of the 

34 possible cause and impact of the events on the data obtained. 

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

36 Reporting Subcommittee of the Organization of Scientific Area Committees for Forensic 

37 Science. 

38 All hyperlinks and web addresses shown in this document are current as of the 

39 publication date of this standard.

40 Keywords: contamination, failed control, reporting DNA results, DNA interpretation
2020-S-0004 Standard for Interpreting, 

Comparing and Reporting DNA Test Results Associated with 

Failed Controls and Contamination Events

41 Table of Contents

42 1 Scope

43

44 2 Normative References

45

46 3 Terms and Definitions

47

48 4 Requirements

49 Annex A (informative) Supplemental Information – Foundational Principles 3

50 Annex B (informative) Supplemental Information – Examples 5

51 Annex C (informative) Bibliography
Standard for Interpreting, Comparing and Reporting DNA Test Results 

Associated with Failed Controls and Contamination Events

52 Standard for Interpreting, Comparing and Reporting DNA test Results 

53 Associated with Failed Controls and Contamination Events

54 1 Scope

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

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

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

58 be relevant to an investigation. These standards may be applied to any type of forensic DNA testing 

59 technology and methodology when conducted in an accredited forensic laboratory.

60

61 2 Normative References

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

63 references.

64 3 Terms and Definitions

65 For purposes of this document, the following definitions apply.

66 3.1

67 comparison

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

69 difference.

70

71 3.2

72 contamination 

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

74 evidence; the exogenous DNA or biological material could be present before the sample is 

75 collected, or introduced during collection or testing of the sample.

76 3.3

77 failed control

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

79

80 3.4

81 forensic sample

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

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

84 carried away from the crime scene. 

85

86 3.5

87 interpretation

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

89 assumptions related to mixtures and single source profiles, distinguishing between alleles 
Standard for Interpreting, Comparing and Reporting DNA Test Results 

Associated with Failed Controls and Contamination Events

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

91 determining whether the data are suitable for comparison.

92

93 3.6

94 negative control 

95 An analytical control that consists of the reagents used in various stages of testing 

96 without the introduction of sample; no results are expected from a negative control. For 

97 DNA testing, negative controls include, but are not limited to, extraction blanks/reagent 

98 blanks and amplification blanks. A negative control in DNA testing is used to detect 

99 contamination introduced into the assay during the testing process via reagents, 

100 disposables or handling errors (which may impact the results observed from samples 

101 tested at the same time).

102

103 3.7

104 positive control 

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

106 control consists of the test reagents and a known sample that will provide an expected 

107 positive response with the test. For DNA testing, positive controls may include, but are 

108 not limited to, extraction positive controls and positive amplification controls.

109

110 3.8

111 reference sample 

112 Biological material obtained from a known individual and collected for purposes of 

113 comparison to evidentiary samples. 

114

115 3.9

116 suitable for interpretation 

117 Data deemed appropriate for interpretation (3.5) based on the laboratory’s validation 

118 studies and documented and verified interpretation protocol. 

119

120 3.10

121 unsuitable for comparison 

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

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

124 requirements. This decision is based on the laboratory’s validation studies and 

125 documented and verified interpretation and comparison protocol.

126

127 4 Requirements

128 4.1 The laboratory protocol shall define what constitutes:

129

130 4.1.1Contamination in a negative control

131

132 4.1.2Contamination in a positive control

133

134 4.1.3Contamination in forensic or reference sample DNA test results

135

136 4.1.4A failed positive control
Standard for Interpreting, Comparing and Reporting DNA Test Results 

Associated with Failed Controls and Contamination Events

137

138 4.1.5A failed negative control

139

140 4.2 The laboratory shall perform and document the assessment of the integrity of the associated 

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

142 shall be based on scientifically valid principles in DNA analysis and include, as appropriate, a 

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

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

145 with re-testing.

146

147 4.2.1 If the DNA test results are determined to be suitable for interpretation within the constraints 

148 of the laboratory's internal validation studies and documented interpretation and comparison 

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

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

151

152 4.2.2 If the DNA test results are determined to be compromised to the extent of being unsuitable 

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

154 interpretation according to laboratory policy.

155

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

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

158 interpretations and comparisons, as appropriate, from both the original and second tests. 

159

160 4.3 When reporting interpretations and comparisons impacted by a failed control or contamination 

161 event, the report shall identify the associated DNA test results and a description of the nature of the 

162 event.

163

164 4.4 The laboratory shall have a written protocol for the release of identifying information for the 

165 source of the contamination.

166

167 4.5 The case record for each sample associated with a failed control or contamination event must 

168 include documentation of the following for the affected sample(s), as applicable:

169

170 4.5.1 The forensic sample, reference, or control DNA test result that failed or was contaminated.

171

172 4.5.2 The likely or known source of contamination.

173

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

175 permitted by law and agency policies.

176
Standard for Interpreting, Comparing and Reporting DNA Test Results 

Associated with Failed Controls and Contamination Events

177

178

179 4.5.3 The likely or known cause of the failed control or contamination.

180

181 4.5.4 The impact of the failed control or contaminant on the integrity of the DNA test results.

182

183 4.5.5 The determination of whether an affected DNA test result is suitable, or unsuitable, for 

184 interpretation. 

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205
Standard for Interpreting, Comparing and Reporting DNA Test Results 

Associated with Failed Controls and Contamination Events

206 Annex A

207 (informative)

208 Supplemental Information – Foundational Principles

209 When polymerase chain reaction (PCR) testing was introduced into crime laboratories in the early 

210 1990s, many of the initial issues encountered by researchers using the highly sensitive PCR testing 

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

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

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

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

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

216 received and processed by the laboratory. When the laboratory identifies instances where the DNA 

217 test results may be compromised, the laboratory follows required procedures for establishing the 

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

219 step is critical in that the DNA test results may still be valid and further interpretation may provide 

220 valuable information, such as exculpatory evidence.

221

222 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] 223 . This control 

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

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

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

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

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

229 control indicates the testing process(es) monitored by the control(s) performed correctly.

230

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

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

233 working correctly). Similar issues may have occurred with the associated samples. When it is not 

234 possible to use the results due to a concern of accuracy, then retesting starting from a point before 

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

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

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

238 “inconclusive” due to the control failure.

239

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

241 with the other DNA test results processed with the control seemingly unaffected. This may occur, 

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

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

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

245 of this standard without retesting all of the samples involved.

246

247 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] 248 . One negative control, 

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

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

251 started at the amplification step for each set of samples undergoing amplification together. These 

252 two negative controls are processed throughout each step of the DNA test alongside the associated 

253 samples. These two controls consist of all reagents, solutions, consumable materials, etc. used during 

254 the DNA testing process, and it is expected that the negative controls meet the laboratory’s definition 
Standard for Interpreting, Comparing and Reporting DNA Test Results 

Associated with Failed Controls and Contamination Events

255 for suitable performance when evaluated at the end of the testing. When contamination is identified, 

256 the laboratory is responsible for evaluating the likely biological source of the contamination and 

257 assessing when and how the event most likely occurred.

258

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

260 presence in or effect on any of the other samples tested. This single contamination event may be 

261 due to any number of reasons where DNA could be introduced only into a single sample, for 

262 example, its presence in or on a consumable material used in the laboratory during testing (e.g., 

263 pipet tip, tube). In other situations, the contaminating DNA may be detected in the profiles from 

264 other samples tested along with the control(s) but be present at such a low level that it has 

265 minimal to no impact on the quality of the DNA test results obtained from the tested sample (e.g., 

266 DNA profile from a high quality single source or two person mixed DNA profile with a very low 

267 level minor component consistent with the profile in the negative control and possibly other 

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

269 for comparison according to established laboratory protocols in accordance with the requirements 

270 listed in this document.

271

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

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

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

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

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

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

278 Recommendations for the Management and Use of Quality Assurance DNA Elimination Databases 

279 in Forensic DNA Analysis). Similarly, some laboratories compare the data obtained within certain 

280 test batches to screen for possible contamination events that may have occurred between DNA 

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

282 may be identified. In this situation, it may be possible to evaluate the DNA test results even in the 

283 presence of contaminating DNA from a known individual, similar to the interpretation steps used 

284 to evaluate mixed DNA test results when a known contributor to a DNA mixture is assumed. The 

285 use of an assumed contributor in the interpretation and comparison of the data should be 

286 reported according to the laboratory’s protocol and best practice recommendations for reporting 

287 evaluations performed using assumed contributors. 

288

289 Additional standards and best practice recommendations are referenced in the Bibliography 

290 that may be used in conjunction with this standard and provide additional useful information
Standard for Interpreting, Comparing and Reporting DNA Test Results 

Associated with Failed Controls and Contamination Events

291

292 Annex B

293 (informative)

294 Supplemental Information – Examples

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

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

297 this standard:

298

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

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

301 quantitation results. The laboratory investigates and determines the most likely cause was 

302 that the analyst did not add the known DNA to the amplification positive control sample. A 

303 surrogate control (in this example, a positive control from the previous day’s run on the 

304 same electrophoresis instrument), was used to confirm that the allele calling was 

305 performed correctly by the software and the profiles were interpreted and used for 

306 comparison purposes. The issue and resolution were documented in the case record and 

307 the results were reported per the laboratory protocol since the results were not directly 

308 impacted by the failed control.

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

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

311 was the individual who performed the latent print examination on the sample prior to the 

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

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

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

315 the report.

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

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

318 DNA extract were consumed during testing. Investigation could not determine the cause of 

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

320 reagents themselves were contaminated). The results for the forensic sample were 

321 reported as not suitable for comparison purposes. Since the contamination event directly 

322 impacted the interpretation of the profile from the forensic sample, the contamination 

323 event was described in the report. 

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

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

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

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

328 interpretation of mixtures of greater than four individuals. No retesting was performed; the 

329 forensic sample profile was reported as not suitable for comparison purposes due to the 

330 high number of contributors.

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

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

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

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

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

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

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

338 6. The DNA profile of the technician who performed amplification set up was detected in 
Standard for Interpreting, Comparing and Reporting DNA Test Results 

Associated with Failed Controls and Contamination Events

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

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

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

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

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

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

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

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

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

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

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

350 second sampling of the neckline of the shirt.
Standard for Interpreting, Comparing and Reporting DNA Test Results 

Associated with Failed Controls and Contamination Events

351 Annex C

352 (informative)

353 Bibliography

354 1] Forensic Science Regulator. Forensic Science Providers: Codes of Practice and Conduct.

355 2014. Available at https://www.gov.uk/government/collections/forensic356 science- providers-codes-of-practice-and-conduct

357

358 2] SWGDAM Contamination Prevention and Detection Guidelines for Forensic 

359 DNA Laboratories. Available at www.swgdam.org

360

361 3] Federal Bureau of Investigation. Quality Assurance Standards for Forensic DNA 

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

363

364 4] ISO/IEC 17025 Testing and Calibration Laboratories. Current version available at 

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

366

367

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

369

370 5] OSAC Proposed Standard 2020-N-007, Best Practice Recommendations for the 

371 Management and Use of Quality Assurance DNA Elimination Databases in Forensic 

372 DNA Analysis; Current version available at 2020-N-007, Best Practice 

373 Recommendations for the Management and Use of Quality Assurance DNA 

374 Elimination Databases in Forensic DNA Analysis. (accessed February 22, 2021)

375 [Update link]

376

377 6] ANSI/ASB Standard 136, Forensic Laboratory Standards for Prevention, Monitoring, 

378 and Mitigation of DNA Contamination, Ed. #1 (currently in review at ASB; has been out 

379 for public comments)

380

381 7] ANSI/ASB Standard 018, Validation Standards for Probabilistic Genotyping Systems First 

382 Edition, 2020 http://www.asbstandardsboard.org/wp383 content/uploads/2020/07/018_Std_e1.pdf (accessed October 2020)

384

385 8] ANSI/ASB Standard 020, Standard for Validation Studies of DNA Mixtures, and 

386 Development and Verification of a Laboratory’s Mixture Interpretation Protocol, First 

387 Edition, 2018 https://asb.aafs.org/wp-content/uploads/2018/09/020_Std_e1.pdf

388 (accessed December 2020)

389

390 9] ANSI/ASB Standard 040, Standard for Forensic DNA Interpretation and 

391 Comparison Protocols, First Edition, 2019 

392 http://www.asbstandardsboard.org/wp393 content/uploads/2019/10/Std_040_e1.pdf (accessed December 2020)

394

395 10] ANSI/ASB Standard 139, Reporting DNA Conclusions (currently in review at ASB; has been 

396 out for public comments)