Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (771 page)

   Maternal hypoparathyroidism

   Hypermagnesemia (e.g., magnesium for treatment of toxemia of pregnancy)

   Magnesium deficiency

   Toxic shock syndrome

Temporary hypocalcemia after subtotal thyroidectomy in >40% of patients; >20% are symptomatic.

   Limitations

   Total serum protein and albumin should always be measured 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 1.0 g/dL that serum albumin falls below 4.0 g/dL; binding to globulin only affects total calcium if globulin >6 g/dL.

   Serum levels increased by

   Hyperalbuminemia (e.g., multiple myeloma, Waldenström macroglobulinemia)

   Dehydration

   Venous stasis during blood collection by prolonged application of tourniquet

   Use of cork-stoppered test tubes

   Hyponatremia (<120 mEq/L), which increases the protein-bound fraction of calcium, thereby slightly increasing the total calcium (opposite effect in hypernatremia)

   Serum levels decreased by