PTH and Hypercalcemia: Serum inactive 25(OH)D levels >100 ng/mL (250 nmol/L) have been defined as hypervitaminosis D, whereas serum levels >150 ng/mL (375 nmol/L) have been proposed to define vitamin D intoxication by the Endocrine Society.(14) Other laboratory findings include hypercalcemia, hypercalciuria, and very low or undetectable parathyroid hormone (PTH) levels.