hypophosphatemia

Hypophosphatemia is a medical condition characterized by a low level of phosphate in the blood. In adults, serum phosphate below about 2.5 mg/dL (0.81 mmol/L) is generally considered low, though reference ranges can vary by laboratory. Phosphate is essential for energy production, muscle function, and bone mineralization, so marked or prolonged deficiency can have systemic effects.

Causes of hypophosphatemia are diverse and typically fall into categories of decreased intake or absorption, increased renal excretion, or a shift of phosphate from extracellular to intracellular compartments. Intracellular shifts occur with insulin administration, refeeding after starvation, acute carbohydrate loads, and certain acid–base disturbances. Renal phosphate wasting can result from hyperparathyroidism, Fanconi syndrome, diuretic use, certain medications, or genetic disorders. Malabsorption, vitamin D deficiency, alcoholism, and poor nutritional status also contribute. Severe illness or sepsis and refeeding syndrome after prolonged starvation are common contexts in which hypophosphatemia occurs.

Clinical features range from asymptomatic to marked weakness, fatigue, and impaired muscle function, including respiratory and diaphragmatic weakness. Other manifestations may include hemolysis, leukocyte dysfunction, arrhythmias related to electrolyte disturbances, bone pain, and osteomalacia with chronic disease.

Diagnosis relies on serum phosphate measurement and assessment of related minerals (calcium, magnesium) and parathyroid hormone, vitamin D status, and renal handling of phosphate. Urinary phosphate excretion can help differentiate renal loss from intracellular shift or poor intake.

Treatment targets the underlying cause and the phosphate deficit. Mild cases may respond to oral phosphate supplementation; moderate to severe cases or those with symptoms require cautious intravenous phosphate repletion, with careful monitoring for hypocalcemia and electrolyte shifts. Refeeding syndrome demands gradual caloric advancement and proactive phosphate support. Long-term management depends on the underlying condition, with specific therapies available for inherited hypophosphatemia.