Undetectable serum calcidiol: not everything that glitters is gold

There is an increased awareness of the adverse consequences of nutritional vitamin D deficiency. We report a patient with chronic tophaceous gout, chronic kidney disease (CKD) Stage 3/4 and undetectable serum calcidiol who developed severe hypercalcaemia upon vitamin D supplementation despite serum 25(OH) vitamin D within the normal range. Upon recovery, serum 1,25(OH)2 vitamin D remained in the normal range despite CKD and serum 25(OH) vitamin D 6 ng/mL. Gout tophi biopsies from additional patients showed macrophage expression of 25(OH) vitamin D 1α-hydroxylase. This case illustrates the dangers of supplementing vitamin D in patients with low serum 25(OH) vitamin D and increased 1α-hydroxylase activity due to granulomatous disease.