ANALYTICAL AND CLINICAL-PERFORMANCE CHARACTERISTICS OF TANDEM-MP OSTASE, A NEW IMMUNOASSAY FOR SERUM BONE ALKALINE-PHOSPHATASE

The performance characteristics of the Tandem(R)-MP Ostase(R) assay, a new microplate immunoassay for bone-specific alkaline phosphatase (bo ne ALP; EC 3.1.3.1) in human sera, are described. Bone ALP is bound to streptavidin-coated microwells by a single biotinylated anti-bone ALP monoclonal antibody. Antigen Is detected by the addition of p-nitroph enyl phosphate. The assay is performed at room temperature in <90 min. Imprecision was 2.3-6.1% with a detection limit of 0.6 mu g/L. Method comparison of bone ALP measurements with the Tandem-MP Ostase assay a nd the mass-based Tandem-R Ostase assay (n = 285) indicated regression statistics of Tandem-MP Ostase = 1.03 Tandem-R Ostase +0.22 mu g/L, S -y/x = 4.0 mu g/L, r = 0.97. Serum bone ALP values in apparently healt hy men and in pre- and postmenopausal women were also similar between the two Ostase assay formats. Liver ALP reactivity determined using th e slope and heat inactivation methods was similar in both Ostase assay s. Liver ALP reactivity ranged from 3 mu g/L (heat inactivation) to 6 mu g/L (slope method) per 100 U/L of liver ALP activity, whereas bone ALP reactivity was 37 mu g/L per 100 U/L of bone ALP activity, indicat ing a liver ALP relative reactivity of 8.1-16.2%. Similar results were obtained with the Alk-phase-B bone ALP immunoassay. The Tandem-MP Ost ase bone ALP assay demonstrated increased concentrations of serum bone ALP in conditions where bone metabolism is increased and showed a rap id, temporal decrease in serum bone ALP in Paget disease patients on b isphosphonate therapy. In conclusion, the Tandem-MP Ostase assay for s erum bone ALP is a rapid, simple, robust nonisotopic alternative to th e Tandem-R Ostase immunoradiometric assay that provides an accurate an d sensitive assessment of bone turnover.