 1. If treated with active vitamin D alone, the participant must be taking 0.5 microgram per day mcgday of calcitriol or 1.0 mcgday of alfacalcidol. If treated with less than 0.5 mcgday of calcitriol or 1.0 mcgday of alfacalcidol, the participant must have a history of inability to be successfully managed with a higher active vitamin D dose. 