What is the reference method and substrate for ACP measurement?

• A. Roy method using thymolphthalein monophosphate
• B. Babson method with alpha-naphthyl phosphate
• C. Szasz method with gamma-glutamyl p-nitroanilide
• D. Tartrate inhibition method

Answer: (A)

The test is asking for the standard reference procedure and substrate used to measure acid phosphatase activity. Historically, the reference method uses Roy’s method with thymolphthalein monophosphate as the substrate. In this setup, ACP hydrolyzes thymolphthalein monophosphate to thymolphthalein, which in alkaline conditions develops a distinct color that can be read spectrophotometrically. This combination—Roy method plus thymolphthalein monophosphate—provides a well-standardized, reproducible assay that labs rely on as the reference. Other approaches use different substrates (for example, alpha-naphthyl phosphate in another method) or use tartrate inhibition to distinguish isoforms, but those are not the reference method and substrate.