Serum phosphorus level:
(1) Patients with the phosphorus depletion syndrome tend to have severe hypophosphatemia, with the serum phosphate < 1 mg/dL (0.323 mmol/L).
(2) A person may have intracellular phosphate depletion yet low or normal serum phosphate levels if there is a shift from intracellular to extracellular stores, as occurs in diabetic ketoacidosis.
(3) A person with a low serum phosphate level may have adequate intracellular stores if there has been an intracellular shift, as occurs with respiratory alkalosis or after a glucose load.
Basis:
(1) depletion of ATP in muscle
(2) depletion of 2,3-diphosphoglycerate in erythrocytes, resulting in increased hemoglobin affinity for oxygen with tissue hypoxia
Patients at risk:
(1) chronic alcoholics
(2) severe malnourishment
(3) diabetes mellitus
(4) severe chronic renal wastage
Triggering events:
(1) feeding a severely malnourished person without phosphorus replacement
(2) ketoacidosis (alcoholic or diabetic)
(3) respiratory alkalosis (with intracellular phosphate shift)
(4) long term use of calcium or magnesium containing antacids
Manifestations:
(1) hematologic: hemolytic anemia, impaired function of white blood cells and platelets
(2) myopathy: muscle weakness, heart failure, rhabdomyolysis
(3) neurologic: metabolic encephalopathy, ranging from confusion to coma
(4) respiratory failure: from diaphragmatic failure
(5) impaired bone mineralization
