Phosphorus, Serum

Serum phosphorus levels in isolation are of limited diagnostic value and should be correlated with serum calcium levels. An increased phosphorus with decreased calcium suggests either hypoparathyroidism or renal disease. A decreased phosphorus and an increased calcium suggests hyperparathyroidism or sarcoidosis. When both calcium and phosphorus are decreased, diagnostic considerations include malabsorption, vitamin D deficiency and renal tubular acidosis. Increased phosphorus and normal or increased calcium suggests milk-alkali syndrome or hypervitaminosis D.