Serum levels of bone-specific alkaline phosphatase and procollagen type I carboxyterminal peptide in vitamin D deficiency

Vitamin D deficiency in adults causes osteomalacia where there is a defect in bone mineralization resulting in an excess of unmineralised osteoid in the bone matrix. The aim of this study was to evaluate the markers of bone formation: total (TALP), bone-specific alkaline phosphatase (BSALP) and procollagen type I carboxyterminal peptide (PICP) in vitamin D deficiency. We studied 100 vitamin D deficient subjects and 82 gender-matched controls. Vitamin D deficiency was defined as serum 25-hydroxyvitamin D level of less than 7 ng/ml, and greater than 10 ng/ml for normal controls. Serum TALP assay was performed by a standard automated method, BSALP and PICP were measured by enzyme immunoassays (Metra Biosystems) and vitamin D by radioimmunoassay. There was significant difference in the TALP between female vitamin D deficient and control subjects (mean +/- sem = 99.8 +/- 8.2 vs 70.5 +/- 2.8 iu/l, p<0.001). Elevated serum TALP (>130 iu/l) was found in 20% (20/100) of the vitamin D deficient patients. There were no significant differences in BSALP or PICP between vitamin D deficient patients and gender-matched control subjects. There was no correlation between vitamin D and PICP in patients but in control subjects, a significant negative correlation (r= -0.431, p<0.0001) was found. In conclusion, although elevated TALP was observed in a minority of vitamin D deficient patients, it is a better marker than PICP. The lack of PICP response in vitamin D deficient subjects suggests the possibility of vitamin D deficiency leading to a block in osteoblast differentiation.