Prostate-Specific Antigen (PSA / P30)
Definition
A glycoprotein produced by the prostate gland and secreted into seminal plasma at high concentrations. The PSA immunochromatographic strip test is the standard confirmatory test for semen in many national laboratories and is valid even when no spermatozoa are recovered.
- Also known as
- p30, gamma-seminoprotein, kallikrein-3
- Source
- Prostate gland, secreted in seminal plasma
- Test format
- Immunochromatographic lateral-flow strip
- Works without sperm
- Yes, valid in vasectomised or azoospermic donors
- Sub-field
- Forensic serology, biological evidence screening
Common questions
Why is a PSA test still run when sperm are already seen microscopically?+
Microscopy confirms sperm cells but a PSA strip independently confirms the fluid is semen, which matters for mixed or degraded stains and for cases where spermatozoa are absent, such as after vasectomy.
Can PSA come from a source other than semen?+
PSA is present at much lower levels in some other body fluids and in a minority of female urine or breast milk samples, so a positive strip is treated as strong but not absolute confirmation and is interpreted alongside case context.
Does a PSA-positive result identify a specific individual?+
No. PSA testing only confirms the presence of semen, it carries no individualising information; DNA profiling of the same stain is needed to link it to a person.
Related terms
- ABAcard P30 (HemaTrace P30)
- A lateral-flow immunochromatographic card that detects PSA at approximately 0.2-4 ng/mL of extract. Widely used in sexual assault kit triage because it...
- Acid Phosphatase (AP)
- An enzyme present at high concentrations in seminal plasma. The Brentamine Fast Violet B (or SERI AP) spray test detects acid phosphatase...
- Amylase
- An enzyme that breaks down starch and is present at high activity in saliva. The Phadebas press test and starch-iodine method detect...
- Confirmatory Test
- A test with sufficient specificity to establish the identity of a biological fluid for reporting purposes. Examples include Takayama and Teichmann crystal...
- Luminol
- A chemiluminescent reagent (5-amino-2,3-dihydro-1,4-phthalazinedione) that produces blue-white light on contact with haemoglobin-derived iron. Detects blood diluted to 1:10,000,000 or more. Used as...
- Presumptive Test
- A fast, low-cost, class-specific screen used to triage a caseload before instrumental work begins. Examples are Marquis reagent for opioids and amphetamines,...
- RSID-Semen
- Rapid Stain Identification of Semen: an immunochromatographic lateral-flow strip from Independent Forensics that detects semenogelin I and II with sensitivity to approximately...
- Semenogelin I and II
- High-molecular-weight proteins secreted by the seminal vesicles that form the semen coagulum immediately after ejaculation. PSA then cleaves them to liquefy the...
- Sensitivity and Specificity in Forensic Context
- Sensitivity is the probability of a positive result when semen is truly present; specificity is the probability of a negative result when...
- Seratec PSA Semiquant
- A lateral-flow PSA strip with a semi-quantitative band-intensity scale. Line intensity corresponds approximately to 1 ng/mL, 2 ng/mL, or greater concentrations, useful...
Explained in these topics
- Biological Sample Screening and Presumptive Tests
- p30/PSA and RSID-SemenA 33-kDa serine protease encoded by the KLK3 gene, secreted by prostate epithelial cells into seminal plasma at 0.5-2 mg/mL. Detected in forensic stain extract...