Reactivity of the RSID™-Saliva test to α-amylase present in vaginal secretions

Presumptive identification of saliva on exhibits collected in relation to sexual offences can provide pivotal evidence regarding specific activities which may have occurred. The immunochromatographic test, RSID™-Saliva, is often employed for this purpose and is reported to be highly specific for α-amylase present at high levels in human saliva. However, a concerning level of positive RSID-Saliva tests to vaginal secretions on the inner crotch of worn underwear was recently reported. Our study aimed to investigate this further using internal vaginal swabs and labial wipes from 30 female donors. The effect of a 1 and 2 hour sample incubation time on the number of positive reactions was also investigated. Positive reactions were observed in 3% of samples which was much lower than previously reported. Positive reactions were not detected for internal vaginal swabs when the incubation time was capped at 1 h and the RSID-Saliva test appeared suited for this application. Caution should be exercised when using the RSID-Saliva test for external samples as the risk of positive reactions appeared higher and was possibly due to cross-contamination with urine and faeces. The effect of shorter sample incubation times on detection of non-saliva biological fluids with the RSID-Saliva test should be investigated.