2 BONE ALKALINE-PHOSPHATASE ASSAYS COMPARED WITH OSTEOCALCIN AS A MARKER OF BONE-FORMATION IN HEALTHY ELDERLY WOMEN

Serum bone alkaline phosphatase (ALP; EC 3.1.3.1) was measured with a wheat germ agglutinin (WGA) precipitation assay and with a new IRMA in a group of healthy elderly women. Both assays were correlated with se rum total ALP activity and with osteocalcin. The two bone ALP assays h ave comparable within- and between-run imprecisions (WGA assay within- run CVs 2.6-5.4% and between-run, 4.0-5.1%; IRMA within-run CV 5.0% an d between-run, 3.2%). Comparison of the WGA precipitation assay (x) wi th the IRMA (y) demonstrated a correlation coefficient of 0.87 [Deming regression equation: y = (0.58 +/- 0.02)x - (4.62 +/- 0.45); n = 101; S-y/x = 1.26; P <0.001). Correlation studies with osteocalcin and tot al ALP showed correlation coefficients (all P <0.001) of 0.34 and 0.65 , respectively, for the WGA precipitation assay and of 0.36 and 0.68, respectively, for the IRMA. We conclude that the two bone ALP assays h ave similar imprecision and that neither can be given preference over the other as a marker of bone turnover.