CA 8.6 - 10.3 LOW

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HYPOCALCEMIA, a serum calcium less than 8. 5 mg/dL. This is a frequent lab abnormality in hospitalized patients and the most common causes include hypoalbuminemia, chronic renal failure, low parathyroid hormone levels or effect, vitamin D deficiency, hypomagnesemia, and alkalosis. Transfusions with citrated blood will also cause hypocalcemia and in this instance, the patient should receive 1 gram of calcium gluconate for every 4 units of blood transfused. Alkalosis increases protein binding of calcium and decreases the free ionized fraction. Hypomagnesemia induces hypocalcemia by causing deficient PTH release and an impaired response of end organ tissues to the hormones effect. The low PTH levels associated with hypomagnesemia return to normal with correction of the low magnesium level. Hypocalcemia associated with renal failure is secondary to precipitation with phosphorous (which is elevated in renal failure), impaired renal conversion of vitamin D to its active form (activation of this vitamin is a two-step process occurring in the liver and then the kidney), renal failure-induced resistance of end organs to parathyroid hormone effect, and decreased intestinal absorption secondary to uremia. Medications, including protamine sulfate, heparin, and glucagon, induce a transient hypocalcemia in some patients. Pancreatitis may cause hypocalcemia of varying degrees, and the calcium level is one of the Ransons criteria in the workup of pancreatitis. Symptoms includes muscle spasm, facial grimacing, seizures, and convulsions. Two signs noted on physical exam are Chvosteks sign (facial spasm elicited by taping on the facial nerve just below the zygomatic arch and in front of the ear) and Trousseaus sign (carpal spasm induced by inflating a sphygmomanometer above the systolic pressure for over 3 minutes).

Corrected serum calcium levels in patients with hypoalbuminemia may be calculated as follows:

Severe symptomatic hypocalcemia should be treated emergently with 10% calcium gluconate 2 ampules intravenously over 10 minutes followed by an infusion of 10% calcium gluconate 60 ml in 500 ml of 5% D5W at a rate of 0.5-2.0 mg/kg/hour. Serial calcium determinations should be made every 4 hours during replacement therapy. The rate of infusion should be adjusted to maintain the serum calcium between 8-9 mg/dL. If hypomagnesemia is present, it must be corrected before attempting to correct the serum calcium. Long-term therapy of hypocalcemia, which is usually associated with hypoparathyroidism, pseudohypoparathyroidism, and chronic renal failure, entails calcium supplementation with calcium carbonate 600 mg 1-2 tablets PO BID/TID. Calcium carbonate may also be given along with oral vitamin D supplements to increase intestinal calcium absorption. The target serum calcium level is between 8-9 mg/dL.