Hypophosphatemia is defined as hypophosphatemia, mainly due to respiratory or metabolic alkalosis. The main clinical manifestations are central nervous system symptoms, such as abnormal sensation, hyperreflexia, tremor, ataxia, and coma, etc. The following differentiation is usually performed. If the cause of alkalosis is ruled out first, urinary phosphate is measured, and if urinary phosphate excretion increases, plasma calcium is measured. If plasma calcium is increased, primary hyperthyroidism and ectopic parathyroid malignancy are the main considerations; if plasma calcium is normal or decreased, secondary hyperparathyroidism, rickets or osteomalacia, Fanconi’s syndrome, and hypophosphatemic chondromalacia are considered. Decreased urinary phosphate excretion should be considered with reduced phosphate intake from food, antacid therapy and insulin therapy.