Concurrent assays of circulating bone Gla-protein and bone alkaline phosphatase: effects of sex, age, and metabolic bone disease.

We measured the serum concentrations of 2 biochemical markers of bone formation, bone Gla-protein (BGP) and bone alkaline phosphatase (BAP), in 164 normal subjects and 164 patients with metabolic bone disorders. The data were reported as Z scores (deviation in SDs from the sex-specific age regression in normal subjects). Both serum BGP and BAP distinguished abnormalities well (mean Z scores for BGP and BAP, respectively) and gave concordant results in patients with hypoparathyroidism (-1.7, -1.4), hyperthyroidism (+1.1, +1.8), primary hyperparathyroidism (+3.6, +2.5), acromegaly (+1.2, +2.8), and postmenopausal osteoporosis (+0.4, +1.9). The 2 markers gave discordant results, however, in patients with glucocorticoid excess (-2.4, +0.9), Paget's disease (+1.8, +41.8), chronic renal failure (+16.3, +0.4), and osteolytic metastases (-1.4, +5.9). These discrepancies may have occurred because serum BGP and BAP concentrations reflect different aspects of osteoblast function or because there are differences in their clearance from the circulation. Consequently, more information is derived about the level of bone formation across the wide range of metabolic bone disorders when both biochemical markers are assayed.