EVALUATION OF AN IMMUNORADIOMETRIC ASSAY FOR BONE ALKALINE-PHOSPHATASE MASS CONCENTRATION IN HUMAN SERA

The performance characteristics of an immunoradiometric assay for bone alkaline phosphatase mass concentration in human sera are reported. W ithin-run imprecision (n = 20) was 12.1% (($) over bar x = 7.8 eta g/l ) and 3.6% (($) over bar x = 22.8 mu g/l), between-day imprecision (n = 8) was 10.1% (($) over bar x = 20.3 mu g/l) and 2.8% (($) over bar x = 84.3 mu g/l). There was a linear relationship between the concentra tions of the standards employed and the counts per minute up to 120 mu g/l. The detection limit was 0.3 mu g/l. In 102 apparently healthy pe rsons (51 males and 51 females; range of age: 18-56 years) the followi ng reference intervals were established: 3.8-21.3 mu g/l (males) and 3 .4-15.0 mu g/l (females). We compared the values obtained using the im munoassay with those obtained by precipitating of bone alkaline phosph atase with wheat-germ lectin (alkaline phosphatase activity concentrat ion was determined at + 25 degrees C by the optimized standard method according to the Recommendations of the German Society for Clinical Ch emistry). For the reference individuals the relationship between the r esults of the two methods is given by the following regression equatio n: Bone alkaline phosphatase activity concentration [U/l] = 14.81 + 3. 28 x bone alkaline phosphatase mass concentration [mu g/l] (r = + 0.78 3). In 89 sera from 32 patients before and after renal transplantation (range of bone alkaline phosphatase mass concentration: 2-39 mu g/l) comparison between the two methods yielded a linear correlation coeffi cient of r = + 0.886. Of 20 sera taken from patients suffering from va rious hepatobiliary diseases (range of total alkaline phosphatase acti vity concentration: 217-3270 U/l) 18 (90%) showed a bone alkaline phos phatase mass concentration above the upper reference limit (range of b one alkaline phosphatase mass concentration: 16-206 mu g/l). This is p robably due to a cross-reactivity of the antibodies employed for the i mmunoassay of bone alkaline phosphatase with liver alkaline phosphatas e in plasma. It is concluded that an increased release of liver alkali ne phosphatase into serum leads to falsely high values for bone alkali ne phosphatase mass concentration, severely limiting the diagnostic va lidity of the test in such cases.