Serum undercarboxylated osteocalcin is a marker of the risk of hip fracture: a three year follow-up study.

We have previously shown that elderly women with an increased serum undercarboxylated osteocalcin (ucOC) level have an increased risk of sustaining a hip fracture as compared to those with normal serum ucOC. We reassessed our findings on a larger number of hip fractures that occurred over 3 years in 183 institutionalized women (aged 70-97 years) belonging to a large prospective clinical trial. Total OC, carboxylated OC, ucOC, and alkaline phosphatase were significantly higher at baseline in those who sustained a hip fracture during the follow-up. The age-adjusted odds ratio for hip fracture was three times higher in women with increased ucOC at baseline (odds ratio = 3.1, 99.9% C.I. = 1.7-6.0, p < 0.001). In the logistic regression, ucOC was still predictive of the hip fracture when age and parathyroid hormone concentration were included into the model (odds ratio = 2.6, 95% C.I. = 1.05-6.4). These data confirm that ucOC is a marker of the increased risk of hip fracture in elderly institutionalized women. Serum ucOC may reflect some nutritional deficiency associated with increased bone fragility.