MEASUREMENT OF SKELETAL SPECIFIC ALKALINE -PHOSPHATASE IN DISORDERS OF CALCIUM-METABOLISM IN CHILDHOOD

Background: Human alkaline phosphatases catalyze the hydrolysis of pho sphate esters at an alkaline pH. Skeletal and liver alkaline phophatas e isoenzymes predominate in serum. During childhood 60-90 % of total p hosphatase are of skeletal origin. The radioimmunometric determination of skeletal alkaline phosphatase in the adult is helpful in the diagn osis of metabolic bone disease. We therefore examined the diagnostic v alue of skeletal phosphatase determination in childhood by using an im munoradiometric assay. Material: We examined the sera of 155 healthy c hildren and adults aged 0-27 years in addition to 82 sera of patients with one of the following diseases: vitamin-D deficient rickets, X-lin ked hypophosphatemic rickets (phosphate diabetes), isolated transient hyperphosphatasia, congenital hypophosphatasia, constitutional delay o f growth and puberty, pubertas praecox, osteopenia of the premature in fant, hepatitis A. Method: The concentration of skeletal phosphatase w as determined by a commercially available immunoradiometric assay (Tan dem(R)-R Ostase(TM). Simultaneously, total alkaline phophatase levels were de termined by photometry and bone-specific alkaline phosphatase was determined by wheat germ agglutinine precipitation. Data were expr essed as standard deviation of the mean. Results: In the normal contro l group alkaline phosphatase values were found to be age dependent wit h elevated levels of skeletal alkaline phosphatase before the age of 1 4 years decreasing to lower adult values after puberty. In children wi th vitamin D - deficient rickets, phosphate diabetes, as well as trans ient hyperphosphatasia and osteopenia of prematurity, skeletal phospha tase values were markedly increased up to 25 standard deviations of th e mean. In two patients with elevated total alkaline phosphatase after a hepatitis A infection, wheat-germ alkaline phosphatase was also ele vated while skeletal phosphatase was within the normal range. In child ren with growth retardation significantly levier values were found in comparision to children with growth accelaration. Correlation of skele tal alkaline phosphatase with total alkaline phosphatase and skeletal alkaline phosphatase assayed by wheat germ agglutinine precipitation w as highly significant (p < 0.01). Conclusion: Due to the finding of a highly significant correlation between skeletal alkaline phosphatase a nd total alkaline phosphatase both in healthy children and in children with various disorders of bone metabolism, measurement of total alkal ine phosphatase is sufficient in most cases to determine bone turnover . In the differential diagnosis of unexplained total alkaline phosphat ase elevation, determination of skeletal alkaline phosphatase may be h elpful.