Evaluation of the RSID (TM)-Saliva test to detect saliva in expirated bloodstains and development of an 'in-scene' protocol

Abstract

The differentiation between bloodstain patterns resulting from impact events and those from the expiration of blood can be crucial to crime scene reconstruction. Physical characteristics used to distinguish impact and expirated bloodstain patterns, are often unclear or absent, making interpretation of some bloodstain patterns difficult. Presumptive tests for salivary α-amylase (SAA) exist; however, these tests are generally unsuited for use at crime scenes or have not been tested on realistic expirated bloodstains. To address this, we assessed the RSIDTM-Saliva test for detecting SAA in expirated bloodstains and developed a modified protocol that can be used in-scene by forensic examiners. Phase 1 experiments, which involved volunteers creating simulated bloodstains by expirating volumes of their own blood onto painted timber boards, produced entirely positive results which demonstrated the test’s efficacy for realistic expirated bloodstains. Phase 2 development and evaluation of a modified in-scene protocol demonstrated that a reduced buffer volume and modified incubation could successfully detect SAA in expirated bloodstains. A significant inverse relationship was observed between the size of a bloodstain and the ‘time-to-positive’. These results support the modified RSIDTM-Saliva test protocol as a viable method to detect SAA in expirated bloodstains in a crime scene environment.