Identification of spermatozoa on sexual assault swabs: a comparative analysis of traditional tube extraction and direct slide elution methods
Spiker, Kolby James
MetadataShow full item record
ABSTRACT The purpose of this study was to compare the efficiency of three sperm elution methods on sexual assault swabs; factors such as solvent type, solvent volume, sperm concentration, and duration of extraction and elution method were evaluated with respect to observed sperm recovery. Swabs containing dilutions of semen ranging from 1:10 to 1:1,000 and simulated post-coital swabs were extracted via the traditional tube extraction, as well as two direct slide elution techniques, tapping and swirling. For the slide elution techniques, a swab cutting was placed directly onto a microscope slide, a small volume of water or buffer was added, and sperm were eluted by either tapping the sample with a stirring stick or swirling it around the slide with metal forceps. The tube method requires a minimum of one and one half hours for extraction, while the slide elution techniques require only ten seconds for extraction. The average sperm counts from 1:10 dilutions processed with the tapping elution method were statistically higher than the 1:10 dilutions samples processed with tube and swirling methods. Elution by tapping also recovered a significantly higher amount of sperm cells from the 1:1,000 dilution compared to the tube extraction of the same dilution. The tapping elution method consistently resulted in the greatest number of spermatozoa observed, followed by the swirling method and then tube extraction; additionally, incidents of false negatives (no sperm observed) were observed with the tube and swirling methods. Simulated post-coital samples produced similar results to the semen samples; however, vaginal swabs from one donor resulted in an extremely high ratio of exfoliated epithelial cells that obscured the spermatozoa, especially with the direct slide elution methods. The slide elution methods resulted in similar and consistent relative standard deviations between dilutions in samples, while the tube extraction results suggest an increase in variance as the dilution increases. Overall, slide elution methods yielded the most observed sperm cells in a significantly shorter amount of time.