MEASUREMENT OF BONE SPECIFIC ALKALINE-PHOSPHATASE IN THE HORSE - A COMPARISON OF 2 TECHNIQUES

For many years total alkaline phosphatase (AP) activity in serum has b een used to monitor bone metabolism in different species. However, tot al AP lacks bone specificity because the total activity in serum is ma de up of several isoenzymes, of which the liver and bone isoforms pred ominate. The aim of the present study was to evaluate an immunondiomet ric assay for measuring bone specific alkaline phosphatase (BAP) in ho rses. BAP, a specific marker of bone formation, was measured in sera f rom thoroughbred horses by using a previously characterised wheat germ lectin (WGL) precipitation assay and an immunoradiometric assay. The levels of immunoreactive BAP (iBAP) and WGL precipitated BAP (wBAP) we re related to the serum levels of total AP and another marker of bone formation, the carboxy-terminal propeptide of type I collagen (PICP). In horses over one year old, iBAP correlated at least as strongly with total AP as with wBAP, which suggests that the immunoradiometric assa y may partially cross-react with liver alkaline phosphatase in horse s erum. This possibility was supported by the observation that there was a weaker correlation between iBAP and PICP than between wBAP and PICP . These data indicate that WGL precipitation is currently the most spe cific method for measuring bone specific alkaline phosphatase in horse s.