Vit D deficiency is a common cause of secondary hyper-parathyroidism. Elevation of PTH level, especially in elderly Vit D deficient adults can result in Osteomalacia, increased bone turnover, reduced bone mass & risk of bone fractures. Low 25-OHVit D concentrations are also associated with lowered bone Mineral density. In conjunction with other biochemical & clinical data, the results may be used as an aid in the assessment of bone metabolism.