Most commonly, hypophosphatemia stems from respiratory alkalosis. (Prolonged, intense hyperventilation can cause severe hypophosphatemia.) Also, increased urine excretion associated with such conditions as hyperparathyroidism, aldosteronism, renal tubular defects, and administration of mineralocorticoids, glucocorticoids, or diuretics may lead to hypophosphatemia.

Other important causes include the use of total parenteral nutrition with inadequate phosphate content, hypercalcemia, diabetic ketoacidosis, chronic alcoholism, and alcohol withdrawal. Forced nutrition of undernourished patients may lead to severe hypophosphatemia.

Rarely, mild hypophosphatemia results from decreased dietary intake. When combined with overuse of phosphate-binding antacids, hypophosphatemia may become severe. Decreased absorption due to such conditions as vitamin D deficiency, malabsorption syndromes, or diarrhea may also cause this condition.

Hyperphosphatemia most commonly results from renal failure with decreased renal phosphorus excretion. It also may stem from overuse of laxatives with phosphates or phosphate enemas, excessive administration of phosphate supplements, and vitamin D excess with increased GI absorption.

Hyperthyroidism may be associated with hyperphosphatemia. Conditions that result in cellular destruction, such as malignant tumors (especially when treated with chemotherapy), cause phosphorus to shift out of the cell and accumulate in extracellular fluid. Respiratory acidosis may also cause such a shift.