Hypophosphatemia

Hypophosphatemia is an electrolyte disorder in which there is a low level of phosphate in the blood. Symptoms may include weakness, trouble breathing, and loss of appetite. Complications may include seizures, coma, rhabdomyolysis, or softening of the bones. Causes include alcohol use disorder, refeeding in those with malnutrition, recovery from diabetic ketoacidosis, burns, hyperventilation, and certain medications. It may also occur in the setting of hyperparathyroidism, hypothyroidism, and Cushing syndrome. It is diagnosed based on a blood phosphate concentration of less than 0.81 mmol/L (2.5 mg/dL). When levels are below 0.32 mmol/L (1.0 mg/dL) it is deemed to be severe. Treatment depends on the underlying cause. Phosphate may be given by mouth or by injection into a vein. Hypophosphatemia occurs in about 2% of people within hospital and 70% of people in the intensive care unit (ICU). Muscle dysfunction and weakness – This occurs in major muscles, but also may manifest as: diplopia, low cardiac output, dysphagia, and respiratory depression due to respiratory muscle weakness. Mental status changes – This may range from irritability to gross confusion, delirium, and coma. White blood cell dysfunction, causing worsening of infections. Instability of cell membranes due to low adenosine triphosphate (ATP) levels – This may cause rhabdomyolysis with increased serum levels of creatine phosphokinase, and also hemolytic anemia. Increased affinity for oxygen in the blood caused by decreased production of 2,3-bisphosphoglyceric acid. Refeeding syndrome – This causes a demand for phosphate in cells due to the action of hexokinase, an enzyme that attaches phosphate to glucose to begin metabolism of glucose. Also, production of ATP when cells are fed and recharge their energy supplies requires phosphate. A similar mechanism is seen in the treatment of diabetic ketoacidosis, which can be complicated by respiratory failure in these cases due to respiratory muscle weakness. Respiratory alkalosis – Any alkalemic condition moves phosphate out of the blood into cells.