4.3.2 25(OH)D and PTH concentrations: Vitamin D status will be measured using a RIA (25-50; Diasorin) that is known to measure both D2 and D3 in plasma (47). This method (RIA) is selected as the now most common clinical method over HPLC and competitive protein binding assays. Serum intact PTH will be measured using an ELISA (50 ul; Immutopics International).