When using cholecalciferol 10,000 IU daily for about 2 weeks, we observed a 40% incidence of mild hypercalcemia (ionized Ca > 1.32 mmol/L) when targeting normal 25-OH vitamin D (30 to 80 ng/mL) for our critically ill trauma patients. When the target was reduced to to > 20 ng/mL, the incidence of hypercalcemia was reduced to 4% which was similar to the 6% incidence of hypercalcemia in our population prior to implementation of vitamin D therapy. We suspect that perhaps free 25-OH vit D was elevated (despite a normal total 25-OH vit D) due to decreased serum albumin and vit D binding protein. However, we do not have the ability to measure free 24-OH vit D nor vitamin D binding protein. Has anyone else done that?