Comparison of modern techniques for saliva screening

Saliva stains present a unique challenge in the forensic setting, often challenging the analyst to weigh the value of presumptive indication of the fluid versus the potential for DNA analysis to yield identification information. There are many situations in which determining the presence of a body fluid is probative and further corroborates DNA evidence. That said, even a minute portion of sample consumed by a screening test could mean the difference between a full, partial, or null profile obtained through DNA analysis. The basis of presumptive testing or screening of saliva has historically been based on the presence of amylase, a component found in relatively high concentrations in human saliva versus other body fluids and substances. Though the current available methods for the screening of saliva in a forensic application have grown in number, the popularity of these methods seemingly has not. This study attempts to identify a specific and sensitive saliva screening test by comparing three modern techniques--the recently released SALIgAE, Phadebas, and starch-iodine mini-centrifuge test--on the basis of sensitivity, specificity, mixtures, and simulated casework samples while also considering sample consumption. The Phadebas method for presumptive saliva testing detected dilutions of neat saliva down to 1:200 versus considerably less sensitive results with SALIgAE and the starch-iodine mini-centrifuge test. Utilizing a screening test with a high degree of sensitivity, such as Phadebas, allows an analyst to gain a maximum amount of information in the form of body fluid indication and DNA results because of the consumption of a small portion of sample.