Comparative examination of three radioimmunoassay kits for human prostatic acid phosphatase

Three commercial radioimmunoassay kits for prostatic acid phosphatase (PAP) were compared on the basis of their ability to measure the enzyme in normal male sera. These kits, issued by Eiken ICL (EIK), Clinical Assays (CLA), and Mallinckrodt (MKT), could measure the serum samples containing PAP above normal levels with precision and reproducibility, and showed excellent linearity on the dilution tests and good correlation with the enzymatic activity. PAP in the serum did not lose immunoreactivity for two weeks if stored below 4 degrees C. However, the sensitivity of CLA and MKT kits should be improved to give reliable values for normal sera with lower PAP contents (less than 1 ng/ml). The upper mean + 2 SD normal limits in ng/ml obtained with these kits were 2.2 (MKT), 2.5 (EIK), and 2.8 (CLA). Some differences in the purity of the standard preparations among these kits were also found. These kits gave different assays values for PAP control sera from CLA and multipurpose QC-RIA sera from Eiken ICL.