Alkaline phosphatase isoenzymes and osteocalcin in serum of normal subjects

Clinical laboratory tests are increasingly being used to evaluate individuals for osteoporosis and other metabolic bone diseases. Serum bone alkaline phosphatase (AP) [EC 3.1.3.1, orthophosphoric-monoester phosphohydrolase (alkaline optimum)] and osteocalcin are used to assess osteoblastic activity. Although methods for assessing relative amounts of AP isoenzymes continuously appear in the literature, no single method is satisfactory for quantification. Polyacrylamide gel electrophoresis with densitometric scanning combined with two-point heat inactivation was used to obtain quantitative values for AP isoenzymes. Serum bone AP concentrations correlated positively and significantly with serum osteocalcin concentrations obtained by radioimmunoassay for women. Men had significantly higher total alkaline phosphatase and bone AP than women, whereas liver AP concentrations did not differ between the two groups. Bone AP correlated negatively and significantly with age in men, but not women. Osteocalcin concentrations tended to be higher in men, but not significantly.