Hypoparathyroidism

Definition

Hypocalcemia, a low bood calcium level, occurs when the concentration of free calcium ions in the blood falls below 4.0 mg/dL (dL=one tenth of a liter). The normal concentration of free calcium ions in the blood serum is 4.0-6.0 mg/dL.

Description

Calcium is an important mineral for maintaining human helath. It is not only a component of bones and teeth, but is also essential for normal blood clotting and necessary for normal muscle and nerve functions. The calcium ion (Ca²⁺) has two positive charges. In bone, calcium ions occur as a complex with phosphate to form crystals of calcium phosphate. In the bloodstream, calcium ions also occur in complexes, and here calcium is found combined with proteins and various nutrients. However, in the bloodstream, calcium also occurs in a free form. Normally, about 47% of the calcium in the blood plasma is free, while 53% occurs in a complexed form. Although all of the calcium in the bloodstream serves a useful purpose, it is only the concentration of free calcium ions which as a direct influence on the functioning of our nerves and muscles. For this reason, the measurement of the concentration of free calcium is more important, in the diagnosis of disease, than measuring the level of total calcium or of complexed calcium. The level of total calcium in the blood serum is normally 8.5-10.5 mg/dL, while the level of free calcium is normally 4-5 mg/dl.

Causes & symptoms

Hypocalcemia can be caused by hypoparathyroidism, by failure to produce 1,25-dihydroxyvitamin D, by low levels of plasma magnesium, or by failure to get adequate amounts of calcium or vitamin D in the diet. Hypoparathyroidism involves the failure of the parathyroid gland to make parathyroid hormone. Parathyroid hormone controls and maintains plasma calcium levels. The hormone exerts its effect on the kidneys, where it triggers the synthesis of 1,25-dihydroxyvitamin D. Thus, hypocalcemia can be independently caused by damage to the parathyroid gland or to the kidneys. 1,25-Dihydroxyvitamin D stimulates the uptake of calcium from the diet and the mobilization of calcium from the bone. Bone mobilization means the natural process by which the body dissolves part of the bone in the skeleton in order to maintain or raise the levels of plasma calcium ions.

Low plasma magnesium levels (hypomagnesia) can result in hypocalcemia. Hypomagnesemia can occur with alcoholism or with diseases characterized by an inability to properly absorb fat. Magnesium is required for parathyroid hormone to play its part in maintaining plasma calcium levels. For this reason, any disease that results in lowered plasma magnesium levels may also cause hypocalcemia.

Hypocalcimia may also result from the consumption of toxic levels of phosphate. Phosphate is a constituent of certain enema formulas. An enema is a solution that is used to cleanse the intestines via a hose inserted into the rectum. Cases of hypocalcemia have been documented where people swallowed enema formulas, or where an enema has been administered to an infant.

Symptoms of severe hypocalcemia include numbness or tingling around the mouth or in the feet and hands, as well as in muscle spasms in the face, feet, and hands. Hypocalcemia can also result in depression, memory loss, or hallucinations. Severe hypocalcemia occurs when serum free calcium is under 3 mg/dL. Chronic and moderate hypocalcemia can result in cataracts (damage to the eyes). In this case, the term "chronic" means lasting one year or longer.

Diagnosis

Hypocalcemia is diagnosed by acquiring a sample of blood serum and measuring the concentraton of free calcium using a calcium-sensitive electrode. Hypocalcemia has several causes, and hence a full diagnosis requires assessment of health of the parathyroid gland, kidneys, and of plasma magnesium concentration.

Treatment

The method chosen for treatment depends on the exact cause and on the severity of the hypocalcemia. Severe hypocalcemia requires injection of calcium ions, usually in the form of calcium gluconate. Oral calcium supplements are prescribed for long term treatment (non-emergency) of hypocalcemia. The oral supplements may take the form of calcium carbonate, calcium chloride, calcium lactate, or calcium gluconate. Where hypocalcemia results from kidney failure, treatment includes injections of 1,25-dihydroxyvitamin D. Oral vitamin D supplements can increase gastrointestinal absorption of calcium. Where hypocalcemia results from hypoparathyroidism, treatment may include oral calcium, 1,25-dihydroxyvitamin D, or other drugs. Where low serum magnesium levels occur, concurrently with hypocalcemia, the magnesium deficiency must be corrected to effectively treat the hypocalcemia.

Prognosis

The prognosis for correcting hypocalcemia is excellent. However, the eye damage that may result from chronic hypocalcemia cannot be reversed.

Prevention

The first, and most obvious, way to help prevent hypocalcemia is to ensure that adequate amounts of calcium and vitamin D are consumed each day, either in the diet or as supplements. The hypocalcemia that may occur with damage to the parathyroid gland or to the kidneys cannot be prevented. Hypocalcemia resulting from overuse of enemas can be prevented by reducing enema usage. Hypocalcemia resulting from magnesium deficiency tends to occur in chronic alcoholics, and this type of hypocalcemia can be prevented by reducing alcohol consumption and increasing the intake of healthful food.

Key Terms

Plasma

Plasma is blood with the cells removed.

Serum

Serum is blood plasma with the blood clotting proteins removed.

Further Reading

For Your Information

Books

• Brody, Tom. Nutritional Biochemistry. San Diego: Academic Press, 1998.
• Zeman, F. and D.M. Dey. Applications in Medical Nutrition Therapy. 2nd ed. Engelwood Cliffs, NJ: Prentice-Hall, 1995.

  Periodicals

• Sutters, M., C.L. Gaboury, and W.M. Bennett. "Severe Hyperphosphatemia and Hypocalcemia: A Dilemma in Patient Management."Journal of the American Society of Nephrology 7 (1996): 2056-2061.

Gale Encyclopedia of Medicine. Gale Research, 1999.