Evaluation of amylase testing as a tool for saliva screening of crime scene trace swabs

Amylase testing has been used as a presumptive test for crime scene saliva for over three decades, mainly to locate saliva stains on surfaces. We have developed a saliva screening application for crime scene trace swabs, utilising an amylase sensitive paper (Phadebas^® Forensic Press test). Positive results were obtained for all tested dried saliva stains (0.5–32 μL) with high or intermediate amylase activity (840 and 290 kU/L). Results were typically obtained within 5 min, and all samples that produced DNA profiles were positive. However, salivary amylase activities, as well as DNA concentrations, vary significantly between individuals. We show that there is no correlation between amylase activity and amount of DNA in fresh saliva. Even so, a positive amylase result indicates presence of saliva, and thereby presence of DNA. Amylase testing may be useful for screening in investigations where the number of DNA analyses is limited due to cost, e.g., in volume crime.     

Development of biological standards for the quality assurance of presumptive testing reagents

Forensic scientists periodically check working test reagents with knowns or standards to verify that the presumptive testing reagents are working properly. Oftentimes, this is done with a neat body fluid such as blood or saliva that is dried onto a swab and kept in a freezer. The problem with this practice is that a degrading test reagent, for example acid phosphatase testing reagent, may test positive on a neat standard but miss a weak semen stain from a case.To ensure that presumptive testing reagents are working properly, a series of “weak” standards have been developed for the testing of acid phosphatase, amylase, creatinine and hemoglobin. The preparation and use of these biological standards will be discussed.