Presumptive Tests for Vaginal Fluids, Research Paper Example

Introduction

In forensics, a screening or presumptive test is a protocol performed in order “to establish the possibility that a specific body tissue or fluid is present” (NFSTC, 2010) on a piece of evidence. By swabbing the evidence and then applying chemicals that react to particular enzymes dominant in the target material to the swab, the test can tell if there is sufficient reason to use confirmatory tests to actually identify the biological material (NFSTC, 2010). The main significance of presumptive tests is that they enable the quick analysis of materials in a crime scene, as opposed to the more rigorous procedures that need to be conducted for confirmatory tests. Thus, presumptive tests enable crime scene investigators to efficiently proceed with the line of investigation using presumptive tests, which would later on be verified in a fully equipped laboratory. In rape investigations, the test can determine the possible presence of vaginal fluids, which can enable authorities to hold a suspect while the sample is sent for further testing.

Given the need for presumptive tests to be used extensively out in the field, it is very important for the tools for the protocol to withstand the hazards of field use and ensure the integrity of the collected sample. Most importantly, the tools should be able to gather sufficient amounts of the sample for testing. Otherwise, there is the risk of the tool giving crime scene investigators false negatives, which would severely affected the progress of the investigation, particularly in the time-sensitive environment of field work (Norris, 2007). However, a problem persists with the use of standard cotton swabs for the protocol. This is that the sample is usually absorbed by the fibers of the cotton and then delivered to its internal mattress core (Benschop et al., 2010). This action traps the sample within the cotton swab, and makes it more difficult to be extracted for confirmatory testing. This means that investigators may find their sample insufficient when they take it back to their laboratory. Worse than that, the use of cotton swabs can actually increase the risk of false negatives.

Results

COPAN (2009) presents the solution to the problem through their specially designed, nylon flocked swabs. A nylon flocked swab uses perpendicular nylon fibers, which induces capillary action in collecting the sample, facilitating strong uptakes of liquid samples (COPAN, 2009). Most importantly, a nylon flocked swab does not have the internal mattress core that the standard cotton swab is burdened with. When the swab picks up the sample, it stays close to the ends of the strands. Even if the sample reaches into the strand, there is nothing on the swab that can permanently absorb it, since its core is just nonabsorbent plastic. As a result, the entire sample collected from the evidence can be used for further testing. This ensures that there would be enough of the sample for use in the laboratory, and decreases the possibility of committing false negative errors.

A study conducted by Benschop et al. (2010) tested the effectiveness of nylon flocked swabs in terms of the volume and integrity of sample gathered from them versus those gathered from traditional cotton flocked swabs. Based on the study’s results, it was established that while the integrity of the sample was preserved in the case of both options, significantly greater volumes of sample were collected from the nylon flocked swabs than from the standard cotton swabs (Benschop et al., 2010). This supports the claims made by COPAN (2009) about the nylon flocked swab and makes this tool a suitable replacement for standard cotton swabs as an upgrade to a crime laboratory’s instruments.

Discussion

However, there are various things to consider whenever the prospect of upgrading from one tool to another is entertained by a laboratory. First is the practicality of the upgrade. While it has been proven in an experimental setting that the nylon flocked swabs do collect a significantly higher volume of sample than the standard cotton swabs, there has yet been no study that compares the actual performance of the two options in a practical setting. While there is evidence supporting that the samples collected by standard cotton swabs do have the risk of being insufficient, this risk is small and can be remedied simply by having a sample taken again in a majority of cases (Norris et al., 2007).  There were no indications in literature found that the probability of getting false negatives from using standard cotton swabs is high, and this variable was not tested in the study of Benschop et al. (2010). Lastly, research by Voorhees et al. (2006) present an alternative to increasing elution using enzymatic digestion while retaining the use of cotton swabs. However, a comparison of costs cannot be conducted since neither Voorhees et al. (2006) nor Benschop et al. (2010) documented such details.

References

Benschop, C., Wiebosch, D., Kloosterman, A., and Sijen, T. (2010). “Post-coital vaginal sampling with nylon flocked swabs improves DNA typing.” Forensic Science International, 4(2): 115-121.

COPAN. (2009). 4N6 DNA Swab Forensic Collection System. Retrieved November 1, 2010 from: http://www.copanswabs.com/products/forensics/

NFSTC. (2010). Presumptive v. Confirmatory Tests. Retrieved November 1, 2010 from: http://www.nfstc.org/pdi/Subject02/pdi_s02_m02_01_a.htm

Norris, J., Manning, K., Linke, S., Ferrance. J., and Landers, J. (2007). “Expedited, chemically enhanced sperm cell recovery from cotton swabs for rape kit analysis.” Journal of Forensic Science, 52: 800–805.

Voorhees, J., Ferrance, J., and Landers, J. (2006). “Enhanced elution of sperm from cotton swabs via enzymatic digestion for rape kit analysis.” Journal of Forensic Science, 51: 574–579.