Presumptive screening of suspected semen stain in situ using cotton swabs and bromochloroindolyl phosphate to detect prostatic acid phosphatase activity.

A novel approach to the presumptive screening of questioned semen stains has been developed which enables the rapid identification of stains which are devoid of semen. Questioned semen stains can be swabbed with a moist cotton swab, and the prostatic acid phosphatase (SAP) activity transferred to the swab identified through assay with 5-bromo-4-chloro-3-indolyl phosphate (BCIP). Controlled laboratory studies revealed that the BCIP swab procedure was as sensitive as the semiquantitative SAP test currently employed in the FBI Laboratory for the presumptive screening of semen stains. A validation study of the BCIP swab procedure in parallel with the current procedure using 4305 case evidence stains indicated that the BCIP swab procedure was as effective as the current procedure in identifying those questioned stains which lack semen. The advantage of the BCIP swab procedure is that it can be performed on questioned stains in situ and thereby avoids the requirement of removing and extracting the stain before assay of SAP activity.