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

ABSTRACT

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.