Validation Study of the “Onestep ABAcard® PSA Test” Kit for RCMP Casework

A comprehensive study into false positive rates for 'other' biological samples using common presumptive testing methods

The identification of biological fluids or materials in forensic samples is a key requirement in forensic science that relies on chemical and biological based tests, most of which exhibit false positivity. When reporting results from such tests, Forensic Scientists use words such as probable, possible, and likely, without always being able to provide robust support for these conclusions. In collating information about false positive rates for a number of these tests, we found limited research into the cross reactions observed from 'other' biological samples in commonly encountered case sample stains. By 'other' we mean biological fluids or materials that are not the primary target of the presumptive test being used. Here we carry out a specificity study to fill gaps in the literature for a number of the presumptive chemical, biological and immunochromatographic tests used to presumptively screen for blood, semen and saliva. The tests selected for this study are the widely used tests: Luminol, TMB/Combur³ Test® E, Kastle-Meyer (KM), RSID™ - Blood, ABAcard® HemaTrace®, Acid Phosphatase (AP), ABAcard® p30, RSID™ - Semen, Phadebas® 'Tube' Test, Phadebas® 'Press' Test, and RSID™ - Saliva tests. Specificity for each of these was tested in known samples, from volunteers, of blood, semen, saliva, urine, sweat, vaginal material, faeces and breast milk, and then false positive rates were determined.

Detection of prostate specific antigen and salivary amylase in vaginal swabs using SERATEC® immunochromatographic assays

Immunochromatographic assays are used by crime laboratories to conduct simple and quick analyses of bodily fluids. These streamlined tests are ideal for decreasing the sexual assault kit backlog in the United States. A large-scale analysis of the frequency of positive results of amylase and prostate specific antigen (PSA) endogenously found in the vaginal cavity was conducted using the SERATEC PSA Semiquant and Amylase tests. Vaginal swabs were self-collected by participants after 7-10 days of no oral contact or male ejaculation. In this study of 50 participants, 98% were negative for PSA and 92% were negative for amylase. Positive results were confirmed to contain no exogenous DNA by male-specific quantitation, short tandem repeat (STR) typing, and Y-STR typing. These results can be used by crime laboratories to help guide interpretation of immunochromatographic test results from vaginal swabs and aid in decision-making in downstream DNA testing.

Biomarker validation of self-reported sex among middle-aged female sex workers in China

PURPOSE

The objective of this study was to examine information bias arising from self-reported sexual activity and its association with syphilitic infections among female sex workers (FSWs) aged 35 years and older in China.

METHODS

A questionnaire was administered to 1245 middle-aged FSWs. Respondents self-reported sexual intercourse in the past 48 hours. The prostate-specific antigen test was used to verify self-reported sexual activity. FSWs were considered discordant if they indicated no sexual intercourse in the past 48 hours on the questionnaire and had a positive prostate-specific antigen test. Logistic regression was used to assess the associations between discordance and syphilis.

RESULTS

Three hundred twenty FSWs self-reported no engagement in sexual intercourse in the past 48 hours. One-fourth of respondents (25%) were discordant. Twenty-two percent and 35.8% of discordant FSWs tested positive for active and prevalent syphilis, respectively. After adjusting for confounders, discordant FSWs had 3.8 times the odds of active syphilis (95% confidence interval: 1.52-9.30) and 2.6 times the odds of prevalent syphilis (95% confidence interval: 1.37-5.02), compared with concordant FSWs.

CONCLUSIONS

FSWs who had active or prevalent syphilis were more likely to be discordant. Data collected via self-reported questionnaire may not be a valid tool to assess sexual behavior.

Exploring discordance between biologic and self-reported measures of semen exposure: a qualitative study among female patients attending an STI clinic in Jamaica

We explored the use of qualitative interviews to discuss discrepancies between two sources of information on unprotected sex: biomarker results and self-reported survey data. The study context was a randomized trial in Kingston, Jamaica examining the effect of STI counseling messages on recent sexual behavior using prostate-specific antigen (PSA) as the primary study outcome. Twenty women were interviewed. Eleven participants were selected because they tested positive for PSA indicating recent semen exposure, yet reported no unprotected sex in a quantitative survey ("discordant"): 5 reported abstinence and 6 reported condom use. Nine participants who also tested positive for PSA but reported unprotected sex in the survey were interviewed for comparison ("concordant"). Qualitative interviews with 6 of the 11 discordant participants provided possible explanations for their PSA test results, and 5 of those were prompted by direct discussion of those results. Rapid PSA testing combined with qualitative interviews provides a novel tool for investigating and complementing self-reported sexual behavior.

Validation of the Seratec® SeraQuant™ for the quantitation of prostate-specific antigen levels on immunochromatographic membranes

Use of immunochromatographic membranes for the detection of prostate-specific antigen (PSA) has become commonplace in forensic laboratories. Experiments were designed to test the newly developed Seratec(®) SeraQuant™ for accuracy, precision, and consistency in the quantitation of PSA. PSA standards were diluted with buffers and run on the instruments. Values obtained were examined for accuracy (was the correct value obtained?) and precision (were multiple sample values consistent?). To test for variation between instruments, large volumes of diluted PSA standard were run repeatedly on six units and the values obtained were plotted against the known PSA values to obtain a standard curve for each instrument. Fifty membranes having negative or weak positive results were then run on the six units, and the adjusted values were recorded and compared. Results of these experiments indicate that the instruments are accurate and precise in the quantitation of low levels of PSA.

Good performance of rapid prostate-specific antigen test for detection of semen exposure in women: implications for qualitative research

BACKGROUND

Prostate-specific antigen (PSA) is a valid biomarker of semen exposure in women and has been used to assess reliability of self-reported sexual behavior as well as serve as a proxy measure for condom efficacy. Quantitative PSA tests are expensive and require specialized equipment. A simple, rapid, and inexpensive test for PSA would facilitate semen biomarker evaluation in a variety of research settings. This study evaluated the performance of a rapid PSA test compared with a quantitative assay to identify semen in vaginal swab specimens.

METHODS

We tested 581 vaginal swabs collected from 492 women participating in 2 separate research studies in Bangladesh and Zimbabwe. PSA in vaginal secretions was detected using the quantitative IMx (Abbott Laboratories) assay and the ABAcard p30 (Abacus Diagnostics) rapid immunochromatographic strip test.

RESULTS

The ABAcard test was 100% sensitive (95% confidence interval [CI], 98%-100%) and 96% specific (95% CI, 93%-97%) compared with the quantitative test in detecting >1.0 ng PSA/mL vaginal swab eluate. Rapid PSA results were semiquantitative and correlated well with PSA concentrations (kappa = 0.88; 95% CI, 0.85-0.90).

CONCLUSION

Rapid PSA detection requires no instrumentation and can be performed easily and economically. Having rapid PSA results available immediately following interview provides opportunities to explore discrepancies between the objective marker of recent semen exposure and self-reported behaviors.

Analysis of body fluids for forensic purposes: from laboratory testing to non-destructive rapid confirmatory identification at a crime scene

Body fluid traces recovered at crime scenes are among the most important types of evidence to forensic investigators. They contain valuable DNA evidence which can identify a suspect or victim as well as exonerate an innocent individual. The first step of identifying a particular body fluid is highly important since the nature of the fluid is itself very informative to the investigation, and the destructive nature of a screening test must be considered when only a small amount of material is available. The ability to characterize an unknown stain at the scene of the crime without having to wait for results from a laboratory is another very critical step in the development of forensic body fluid analysis. Driven by the importance for forensic applications, body fluid identification methods have been extensively developed in recent years. The systematic analysis of these new developments is vital for forensic investigators to be continuously educated on possible superior techniques. Significant advances in laser technology and the development of novel light detectors have dramatically improved spectroscopic methods for molecular characterization over the last decade. The application of this novel biospectroscopy for forensic purposes opens new and exciting opportunities for the development of on-field, non-destructive, confirmatory methods for body fluid identification at a crime scene. In addition, the biospectroscopy methods are universally applicable to all body fluids unlike the majority of current techniques which are valid for individual fluids only. This article analyzes the current methods being used to identify body fluid stains including blood, semen, saliva, vaginal fluid, urine, and sweat, and also focuses on new techniques that have been developed in the last 5-6 years. In addition, the potential of new biospectroscopic techniques based on Raman and fluorescence spectroscopy is evaluated for rapid, confirmatory, non-destructive identification of a body fluid at a crime scene.

The use of Polilight in the detection of seminal fluid, saliva, and bloodstains and comparison with conventional chemical-based screening tests

Biological stains can be difficult to detect at crime scenes or on items recovered from crime scenes. The use of a versatile light source may assist in their detection. The ability of Polilight to locate potential semen, saliva, and blood stains on a range of substrates and at different dilutions was tested. We also tested the use of Polilight in comparison with conventional chemical-based presumptive screening tests such as acid phosphatase (AP), Phadebas, and luminol, often used in casework for detecting potential semen, saliva, and blood stains, respectively. The Polilight was able to locate stains that were not apparent to the naked eye. The color of the material on which a stain is deposited can have an effect on the detectibility of the stain. The Polilight was found to be comparable with the AP and Phadebas tests in terms of its sensitivity. In a comparative study between the AP test and Polilight on 40 casework exhibits, one false-negative result was observed when using the Polilight. On a series of mock casework exhibits it was determined that the Polilight can be used successfully to locate saliva stains for DNA analysis. The sensitivity of luminol for detecting potential bloodstains was greater than that of Polilight; however the Polilight has particular application in instances where a bloodstain may have been concealed with paint. Overall, the Polilight is a relatively safe, simple, noninvasive, and nondestructive technique suitable for use in forensic casework.

Use of Prostate Specific Antigen in the Identification of Semen in Postmortem Cases

Over the past 20 years, the use of prostate specific antigen (PSA) as evidence of the presence of semen in forensic cases has been well established. In this study, we compared a commercially available immunoradiometric assay (IRMA) for the identification of PSA with the identification of spermatozoa in swabs obtained from the vagina of deceased females. There was agreement between the 2 methods in 67 of the 80 cases (84%), including 18 cases where both the PSA was positive and sperm were observed microscopically. The remaining cases had 1 positive result and 1 negative result. We concluded that although there was substantial agreement between the presence of sperm and a positive PSA, there were enough discrepancies between the 2 methods (16%) to justify the use of both methodologies, if possible, to make the determination of sexual activity prior to death.