membrane potential. Calcium levels are increased in hyperparathyroidism (determi-
nation of ionized serum calcium is more useful for the diagnosis of hyperparathy-
roidism), parathyroid hormone injection, hypervitaminosis“D,”prolonged intake of
milk and alkali (the milk-alkali syndrome), multiple myeloma, and polycythemia. It
is also increased in acute and chronic renal failure and osteomalacia with malab-
sorption. Hypocalcemia occurs when serum calcium levels fall below 7 mg/dl.
Hypocalcemia is more serious and life-threatening condition than hypercalcemia.
Calcium levels are decreased in hypoparathyroidism, osteomalacia,
hyperphosphatemia, tetany, renal failure, and nephrotic syndrome. In rickets, the
product of serum calcium and phosphorus decreases usually below 30 mg/dl. An
increase in alkaline phosphatase activity is a characteristic feature of rickets. It is
necessary to measure total serum proteins and albumin levels simultaneously for
proper interpretation of serum calcium levels, since 0.8 mg of calcium is bound to
1.0 g of albumin in serum. To correct, add 0.8 mg/dl for every 1 g/dl that serum
albumin falls below 4 g/dl.
88 21 Estimation of Total Calcium in Serum and Urine