FGF23 and hypophosphatemia: Clinicians need to be aware that severe vitamin D deficiency, defined as an extremely low/undetectable 25(OH)D level (ie, at the detection level of the assay, usually >4 ng/mL), can cause severe proximal muscle weakness independent of secondary hyperparathyroidism‐induced hypophosphatemia.18, 19, 21 Furthermore, the persistently elevated blood levels of I,25(OH)2D generated by granulomas can indirectly affect phosphate metabolism by increasing the production of FGF‐23, which results in hypophosphatemia.