FGF23 and hypophosphatemia: Laboratory evaluation demonstrated profound hypophosphatemia (1.6 mg/dL), markedly elevated FGF23 levels (455 RU/mL), and renal phosphate wasting (tubular reabsorption of phosphate at 35%, tubular maximum phosphate reabsorption per glomerular filtration rate (TmP/GFR) at 1.04 mg/dL).