Optimizing elution times for sexual assault evidence processing
OA Version
Citation
Abstract
Due to the widely known sexual assault kit (SAK) backlog issue in the United States, crime laboratories should seek ways to improve their standard operating procedures (SOPs) to rapidly process SAKs. One simple way to increase efficiency is by utilizing a shorter elution time to release spermatozoa, seminal fluid and saliva from a swab or fabric cutting. There is variation in the amount of time each individual crime lab requires for eluting evidentiary swabs or stains, and clearer guidance in this method would allow analysts to process more SAKs on a regular basis. Additionally, the time spent on microscopic sperm identification is a major obstacle to faster analysis and reporting. The use of an automated microscope, such as the one from MetaSystems® (Heidelberg, Germany), along with their Metafer analysis software may streamline sperm counting and therefore enable analysts to submit evidentiary samples for deoxyribonucleic acid (DNA) analysis sooner. Each of these aspects of routine SAK processing was addressed in this study. Elution times of 15 minutes, 30 minutes, and 60 minutes were used on swabs and cotton swatches stained with semen dilutions to determine if consistent immunoassay card results and microscopic sperm identifications could be obtained with shorter elution times. Microscopic sperm identification was completed manually as well as using an automated microscope to aquire complete sperm counts for each slide. The percent recovery of sperm after each elution time was then statistically compared to determine if using shorter elution times could lead to potentially false negative results. The success and rapidity of the MetaSystems scans and Metafer data were also qualitatively evaluated. The same three elution times were also used on swabs stained with saliva dilutions in an attempt to obtain concordant immunoassay card results across the elutions for both sample types.
The results showed that in both the semen and saliva experiments, a shorter elution time of 15 minutes or 30 minutes rarely led to additional negative immunoassay or sperm identification results compared to the 60-minute elution. The calculated percent recoveries of sperm showed that any longer elutions past the initial 15 minutes did not result in a statistically significant percent of additional sperm cells. Therefore, it would be more beneficial than detrimental for crime labs to employ shorter elution times down to 15 minutes. Finally, based on the extended time required to manually confirm the sperm calls made by the software, it was determined that the automated microscope did not optimize the time required for microscopic sperm counting when clusters of cells were present. However, because most crime labs are concernced with sperm density and not total sperm counts, use of an automated microscope may still be beneficial in casework because of the ability to capture individual sperm cell images and scan multiple slides at one time.
Description
2025