Method for determination of bone alkaline phosphatase activity: analytical performance and clinical usefulness in patients with metabolic and malignant bone diseases.

We report the performance characteristics of an assay for determination of bone alkaline phosphatase (ALP) activity after immunoadsorption in microplate wells. Between-run imprecision was between 7.1% and 11.2%. The detection limit was 1.0 U/L. Comparisons with an immunoradiometric test for determination of bone ALP mass concentrations yielded the following regression equation: y = 3.11 + 1.33x with y, the bone ALP activity concentration (U/L) (and x, the bone ALP mass concentration microgram/L) (r +=0.974, n = 103). Using sera from patients with liver diseases and sera from patients with secondary hyperparathyroidism yielded a cross-reactivity of 20% for circulating liver ALP (and its membrane-bound isoform). In patients receiving renal transplants, Z-score analysis revealed that after transplantation the increase in bone ALP activity is more pronounced than total ALP activity. In tumor patients, receiver-operating characteristic analysis revealed that bone ALP activity shows the same diagnostic efficacy as total ALP activity in the detection of bone metastases (as assessed by bone scintigraphy). In multiple myeloma patients, suppressed osteoblast activity was well detectable by bone ALP activity determination.