Prostatic Acid Phosphatase (PAP)
Definition
The AP isoform secreted by acinar epithelial cells of the prostate gland, found in seminal plasma at concentrations of 25-1,000 U/mL, orders of magnitude above all other body fluids.
- Source
- Acinar epithelial cells of the prostate gland
- Fluid
- Seminal plasma
- Concentration
- 25 to 1,000 U/mL
- Relative level
- Orders of magnitude above other body fluids
Common questions
Why is PAP concentration in semen useful for a presumptive test?+
Because PAP levels in semen are so much higher than in any other body fluid, an acid phosphatase color test on a stain gives a strong positive reaction almost uniquely for semen, making it a fast screening step before confirmatory testing.
Does a positive PAP test alone confirm semen for court purposes?+
No. PAP screening is presumptive, since trace amounts occur in other tissues and the color reaction can be affected by other substances, so a confirmatory test targeting a semen-specific protein such as PSA/p30 or sperm cell identification is required for a definitive conclusion.
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...
- Brentamine Fast Violet B Test
- A two-component spot test in which sodium alpha-naphthyl phosphate (substrate) is hydrolysed by AP to alpha-naphthol, which couples with fast violet B...
- False Positive
- A test result that indicates the presence of a target analyte when it is absent. In forensic serology this may mean incorrectly...
- Fluorescent AP Assay
- A more sensitive format using 4-methylumbelliferyl phosphate (4-MUP) as substrate. AP cleaves 4-MUP to 4-methylumbelliferone, which fluoresces under UV. Useful on aged...
- Quantitative AP Threshold
- A numerical activity level, expressed in units per litre of extract, above which a result is treated as semen-positive. Common thresholds range...