Brentamine Fast Violet B Test
Definition
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 diazonium salt to produce a purple-violet azo dye. A strong colour change within 30 seconds is presumptive positive for semen.
- Type
- Two-component colorimetric spot test
- Target enzyme
- Acid phosphatase
- Reaction time
- Within 30 seconds for a strong positive
- Colour change
- Purple-violet azo dye formation
Common questions
Is a positive Brentamine fast violet B test conclusive proof of semen?+
No, it is a presumptive test because acid phosphatase, while highest in seminal fluid, is also present in lower levels in some vaginal secretions and other body fluids, so a positive result indicates semen may be present and directs the sample toward confirmatory testing.
Why does reaction speed matter when reading this test?+
A strong colour change within 30 seconds indicates high acid phosphatase activity typical of semen, while a slow or weak colour change over several minutes is more consistent with background activity from other sources, so timing helps the examiner judge how much weight to give the result.
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...
- 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...
- Prostatic Acid Phosphatase (PAP)
- 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...
- 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...