Prostate-Specific Antigen (PSA)
Definition
A serine protease glycoprotein (also called p30) secreted in high concentrations by the prostate gland into seminal plasma. The primary immunological marker for semen in forensic casework. Detected by antibody-based assays including ELISA and lateral-flow immunochromatographic strips.
- Also known as
- p30
- Chemical class
- Serine protease glycoprotein
- Source
- Prostate gland, secreted into seminal plasma
- Detection methods
- ELISA, lateral-flow immunochromatographic strips
- Evidence role
- Primary immunological marker for semen
Common questions
Is PSA testing in forensic casework the same test used in medical prostate cancer screening?+
The underlying antigen is the same protein, but forensic serology uses qualitative or semi-quantitative strip and ELISA formats built to confirm presence in a stain, while clinical PSA testing measures precise blood concentration for cancer monitoring, so the assay format and interpretation differ.
Why is PSA testing used alongside sperm cell microscopy rather than replacing it?+
PSA confirms the presence of seminal fluid even without intact sperm, which is essential in cases involving a vasectomized donor or a degraded sample, but combining it with sperm observation when sperm are present gives two independent lines of evidence that strengthen the overall conclusion.
Can PSA levels distinguish between different individuals the way DNA can?+
No. PSA testing only confirms that semen is present in a stain; it carries no individualising information about who deposited it, which is why a positive PSA result is always followed by separate DNA profiling to identify a specific source.
Related terms
- Alpha-Amylase (Salivary Isoform)
- An enzyme present in saliva at concentrations several orders of magnitude higher than in other body fluids. Detected immunologically using anti-human salivary...
- Azoospermia
- The absence of spermatozoa from ejaculated semen, resulting from obstructive causes (vasectomy, ductal blockage) or non-obstructive causes (testicular failure). Azoospermic semen contains...
- Differential Extraction
- A two-step DNA extraction procedure used when a stain contains both sperm cells and non-sperm epithelial cells. The first step lyses epithelial...
- Inhibition Agglutination Assay
- A serological technique for detecting soluble antigens in body-fluid extracts. Known antibody is incubated with the stain extract; if the target antigen...
- Lateral-Flow Immunochromatographic Strip
- A point-of-care format immunoassay in which a sample migrates along a nitrocellulose membrane past a labelled antibody zone and a capture antibody...
- Salivary Amylase
- An enzyme secreted by the parotid, submandibular, and sublingual salivary glands that cleaves starch molecules. Its high concentration in saliva relative to...
- Secretor
- An individual whose ABO blood group antigens are expressed on red blood cells and also released into body fluids such as saliva,...
- Sexual Assault Forensic Examination (SAFE) Kit
- The standardised collection kit used by trained healthcare providers to obtain biological samples from a survivor within a defined collection window, typically...
- Substrate Control
- A sample of the unstained surface material from an area adjacent to a body fluid stain, collected alongside the stain and processed...
- Touch DNA
- Minute quantities of epithelial cells transferred by skin contact with a surface, without leaving a visible stain. Collected by swabbing contact points...
Explained in these topics
- Immunological Methods in Sexual Assault Investigations
- Semen, Saliva and Other Body Fluids as EvidenceA glycoprotein produced by the prostate gland and secreted in high concentrations into seminal plasma. PSA detection confirms the presence of seminal material...