ANALYTICAL AND CLINICAL-EVALUATION OF A METHOD TO QUANTIFY BONE ALKALINE-PHOSPHATASE, A MARKER OF OSTEOBLASTIC ACTIVITY

An immunoradiometric assay (IRMA), involving specific monoclonal antib odies (Ostase, Hybritech) and agarose electrophoresis (Isopal, Beckman ), two methods for quantification of serum bone alkaline phosphatase ( ALP), a marker for osteoblastic activity, were analytically and clinic ally compared in 293 patients: 79 with end-stage renal failure treated with hemodialysis and 214 with malignant disease. Acceptable within-a ssay precision was obtained for the IRMA method: 82.5% of the duplicat e determinations had a coefficient of variation (CV) <5%. Curve fittin g characteristics were bad and the sensitivity was better than the one mentioned by the manufacturer. Overall correlation between the two me thods was good (r=0.92), except (a) for low values of bone ALP and (bi in some samples with high total liver ALP activity. Low bone ALP dete rmined with the IRMA (<5 mu g/L) was confirmed by electrophoresis (<22 U/L), but ALP activity determined by electrophoresis to be low (<22 U /L) was not correlated with the IRMA results. After standardizing our results by computing values for bone ALP, Delta z (= z(ostase) - z(ele ctrophoresis)) was significant correlated with liver ALP activity (r=0 .73, P<0.0001). We conclude that the IRMA for quantifying bone ALP is acceptable. However, when high values for bone ALP are found with the Ostase method confirmation by electrophoresis remains mandatory to rul e out cross-reactivity with high amounts of liver ALP.