P30 (PSA)
Definition
Prostate-specific antigen, a glycoprotein secreted by the male prostate gland and present in semen at high concentrations. ELISA or lateral-flow immunochromatographic tests for p30 are the standard confirmatory method for identifying a stain as semen in forensic laboratories worldwide.
- Also known as
- PSA, seminal glycoprotein
- Source tissue
- Prostate gland
- Detection method
- ELISA or lateral-flow immunochromatographic strip
- Evidence type
- Presumptive to confirmatory semen marker
- Limitation
- Can appear at low levels in some non-seminal fluids
Common questions
Is a positive p30 test proof that semen is present?+
It is treated as strong confirmatory evidence in most labs, but p30 has been detected at trace levels in a small number of non-seminal sources, so some laboratories still pair it with sperm cell observation or additional markers when the result will be central to a case.
Why is p30 tested instead of looking for sperm directly under a microscope?+
Sperm cells degrade quickly or may be absent entirely in a vasectomized donor, so a biochemical marker like p30 can confirm semen even when no intact sperm heads remain visible on a slide.
How fast do lateral-flow p30 tests give a result?+
Most commercial immunochromatographic strips give a visible line within about ten minutes, which is why they are favored for rapid screening at intake before a sample goes on to slower confirmatory serology or DNA work.
Related terms
- 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...
- Alpha-Amylase
- Salivary enzyme. Detected by starch-iodine (clear zone in blue background) or the Phadebas reagent (blue colour from dye-linked starch). Concentration in saliva...
- Barberio Test
- Presumptive semen test. Saturated picric acid reacts with spermine to form yellow rhombic spermine picrate crystals.
- Discriminating Power
- The statistical ability of a typing system to distinguish one individual from another in a given population. Expressed as the probability that...
- Florence Test
- Presumptive semen test. Iodine plus potassium iodide reacts with choline in semen to form dark-brown rhombic / needle-shaped choline iodide crystals.
- Hp, Gc, Tf
- The classical serum-protein polymorphism panel: haptoglobin (binds free haemoglobin; Hp1-1, Hp2-1, Hp2-2 phenotypes), group-specific component (vitamin D binding protein, Gc1F / Gc1S...
- Isoenzyme / Polymorphism
- Different molecular forms of the same enzyme separable by electrophoresis. Forensic polymorphic markers have several common alleles in the population, so a...
- PGM, EsD, AK, GLO
- The classical RBC isoenzyme panel: phosphoglucomutase, esterase D, adenylate kinase, glyoxalase I. All polymorphic, all typed by starch-gel or isoelectric-focusing electrophoresis of...
- Precipitin Test
- A serological method in which an antiserum specific to one species' proteins is mixed with an extract of an unknown specimen. Formation...
- Random Match Probability (RMP)
- The probability that a randomly chosen unrelated person from the relevant population would match the evidence profile by chance. A very small...
- Secretor
- An individual whose ABO blood group antigens are expressed on red blood cells and also released into body fluids such as saliva,...
- Secretor Status
- A genetic trait that determines whether a person expresses their ABO blood group antigens in secreted body fluids such as saliva, semen,...
Explained in these topics
- Body Fluids, RBC Enzymes and Serum Proteins of Forensic SignificanceProstate-specific antigen, a 30 kDa glycoprotein from the prostate. Confirmatory for seminal fluid even in azoospermic or vasectomised donors. Detected by immu...
- The Transition from Serology to DNA Profiling in Forensic Science