Normal serum phosphorus concentration in adults is 0.83 to l.45 mmol/L. When the serum phosphorus concentration is ≤0.8 mmol/L, it is called hypophosphatemia (hypophosphatemia). Serum phosphorus <0.3 to 0.5 mmol/L is considered severe hypophosphatemia. Since most phosphorus is stored intracellularly, serum phosphorus concentration may not be a reliable indicator of total phosphorus in the body. Treatment of hypophosphatemia begins with determining whether the reduced blood phosphorus concentration is a deficiency of total body phosphorus or the result of intracellular transfer of phosphorus (e.g., respiratory alkalosis). History taking, physical examination and laboratory tests help to distinguish the cause of hypophosphatemia. Tests to confirm the diagnosis of hypophosphatemia: 1. The GFR-standardized renal phosphorus threshold (Tmpi=Tmpo4/GFR) is calculated by calculating the renal tubular reabsorption phosphate value (1-Cpo4:Ccr) and measuring the glomerular filtration rate (GFR), with normal values ranging from 2.5 to 4.2 mg/100 ml. 2. Hypophosphatemia patients with reduced Tmpi: it is the kidney's response, usually accompanied by both gastrointestinal loss and intracellular transfer of phosphorus. 3, Increased Tmpi: is indicative of increased renal phosphorus excretion secondary to PTH-mediated, Fanconi syndrome, X-linked hypophosphatemia, autosomal dominant hypophosphatemic rickets, or tumor-associated osteochondrosis.