Patent ID: 7465556

Claim:
An immunoassay method for determining tartrate resistant acid phosphatase 5b (TRACP 5b) in a specimen, the method comprises binding both TRACP 5b and TRACP 5a in the specimen to an antibody that is reactive with both of TRACP 5b and TRACP 5a, separating the TRACP 5a and TRACP 5b bound to the antibody, and subjecting the TRACP 5a and TRACP 5b bound to the antibody to enzyme reaction with a 2-halo-4-nitrophenylphosphoric acid represented by the general formula (1): wherein X is Cl, or a salt of the compound of general formula (I), which is a substrate more specific for TRACP 5b than for TRACP 5a, and then assaying the enzymatic activity of said enzyme reaction to determine TRACP 5b to carry out the immunoassay of TRACP 5b in the specimen, wherein at the time of the enzyme reaction, the pH is higher than 6.3 and not higher than 6.8.