The evaluation of forensic evidence has changed significantly since the 1994 DNA Identification Act. Forensic DNA analysis plays a critical role in criminal investigations, and as a result now presents forensic labs with huge backlog issues due to the number of samples submitted for examination. This is where presumptive testing of evidence, such as suspected biological fluids, can be helpful.
Presumptive tests work by detecting a component of the suspected fluid that is unique to that fluid, or only sparsely found in other fluids or commercial products. The specificity of a presumptive test is dependent upon how unique the component of interest is to a particular fluid.
Presumptive tests can be used with aged stains, diluted stains, and in some cases the aliquot prepared for the presumptive testing can be used again for DNA testing, if necessary. Presumptive tests are quick to perform, and also are an important step in order to decrease DNA backlog by eliminating samples that do not actually contain fluids of interest.
Gateway Analytical currently conducts presumptive testing for the presence of blood, seminal fluid, urine, and saliva. Presumptive testing is advantageous for our customers because they are efficient screening tests, which means a fast turnaround time. In addition, customers can save significantly on cost by having a presumptive test performed rather than sending a non-viable sample to a lab for DNA testing. However, any non-law enforcement personnel should strongly consider having possible criminal or civil samples submitted by an attorney; this will ensure the proper chain of custody.