Evidence collected from a rape or sexual assault victim can be analyzed to identify the presence of male semen.
Materials that can be analyzed:
(1) stains on clothing
(2) vaginal fluid
(3) oral or nasal discharge, swabs or washings
(4) anal swabs
Factors affected recovery:
(1) time since the event
(2) dilution by secretions or environmental fluids
(3) contamination by environmental debris
(4) amount of the original material deposited
(5) exposure to temperature extremes (poor handling of materials)
|
Examination |
Features |
|
demonstration of sperm |
absent in a man with a vasectomy; least sensitive method of detection; may be motile if examined early; with time there is morphologic deterioration |
|
prostatic acid phosphatase |
concentrations in vaginal fluid correlate with time since intercourse during the first 48 hours (Ricci and Hoffman) |
|
prostatic specific antigen (PSA) |
simple, sensitive and reproducible (Simich et al) |
|
p30 (semen glycoprotein of prostatic origin) |
more sensitive and specific than prostatic acid phosphatase and can be detected for a longer period (Graves et al) |
|
polymerase chain reaction (PCR) for Y chromosome |
most sensitive method but false positives a problem; does not prove material is semen; of no value if victim is male |
Interpretation:
• The presence of a positive tests confirms the presence of semen, but does not establish the mechanism.
• The negative test does not exclude rape.
• A positive test for semen can help justify further molecular testing to further characterize the source male.
Limitations:
• A careful rapist may wear a condom and take other steps to reduce the amount of physical evidence available to document the crime.
Specialty: Clinical Laboratory, Emergency Medicine, Obstetrics & Gynecology, Pedatrics
ICD-10: ,
