Calcium is the most abundant mineral in the human body, and is critical to good health. It is not only a component of bones and teeth, but is also essential for blood clotting and necessary for muscle and nerve functions. Calcium plays an indispensable role in cell permeability, formation of bones and teeth, blood coagulation, transmission of nerve impulses, and normal muscle contraction. Nearly all (99%) of the body's calcium is found in the bones. The remaining 1 % exists in ionized form in serum, and it's the maintenance of the 1 % of ionized calcium in the serum that's critical to healthy neurologic function.
The parathyroid glands regulate ionized calcium and determine its resorption into bone, absorption from the GI mucosa, and excretion in urine and stool. Severe calcium imbalance requires emergency treatment because a deficiency (hypocalcemia) can lead to tetany and seizures; an excess (hypercalcemia), to cardiac arrhythmias and coma.
The causes of too little calcium include:
An insufficiency of serum calcium levels, can be caused by hypoparathyroidism, by kidney failure, by low levels of plasma magnesium (hypomagnesia), or by failure to get adequate amounts of calcium or vitamin D in the diet. Hypocalcemia may also result from the consumption of toxic levels of phosphate, found in certain enema formulas.
Too much calcium:
Signs and symptoms
Indications of calcium imbalance depend on the type of imbalance.
A lack of calcium causes nerve fiber irritability and repetitive muscle spasms. Consequently, characteristic symptoms of hypocalcemia include perioral paresthesia, twitching, carpopedal spasm, tetany, seizures and, possibly, cardiac arrhythmias. Although Chvostek's sign and Trousseau's sign are reliable indicators of hypocalcemia, they're not specific.
Clinical effects of hypercalcemia include muscle weakness, decreased muscle tone, lethargy, anorexia, constipation, nausea, vomiting, dehydration, polydipsia, and polyuria. Severe hypercalcemia (serum levels that exceed 5.7 mEq/L) may produce cardiac arrhythmias and, eventually, coma.
A serum calcium level less than 4.5 mEq/L confirms hypocalcemia; a level above 5.5 mEq/L confirms hypercalcemia. (However, because approximately one-half of serum calcium is bound to albumin, changes in serum protein must be considered when interpreting serum calcium levels.)
The Sulkowitch urine test shows increased urine calcium precipitation in hypercalcemia. In hypocalcemia, an electrocardiogram (ECG) reveals a lengthened QT interval, a prolonged ST segment, and arrhythmias; in hypercalcemia, a shortened QT interval and heart block.
An acute imbalance requires immediate correction, followed by maintenance therapy and correction of the underlying cause.
A mild calcium deficit may require nothing more than an adjustment in diet to allow adequate intake of calcium, vitamin D, and protein, possibly with oral calcium supplements. Acute hypocalcemia is an emergency that needs immediate correction by LV. administration of calcium gluconate or calcium chloride.
Chronic hypocalcemia also requires vitamin D supplements to facilitate GI absorption of calcium. To correct mild deficiency states, the amounts of vitamin D in most multivitamin preparations are adequate. For severe deficiency, vitamin D is used in four forms: ergocalciferol (vitamin D2), cholecalciferol (vitamin D3), calcitriol, and dihydrotachysterol, a synthetic form of vitamin D2.
Treatment of hypercalcemia primarily eliminates excess serum calcium through hydration with normal saline solution, which promotes calcium excretion in urine. Loop diuretics, such as ethacrynic acid and furosemide, also promote calcium excretion. (Thiazide diuretics are contraindicated in hypercalcemia because they inhibit calcium excretion. )
Corticosteroids, such as prednisone and hydrocortisone, are helpful in treating sarcoidosis, hypervitaminosis D, and certain tumors. Mithramycin can also lower the serum calcium level and is especially effective against hypercalcemia secondary to certain tumors. Calcitonin may also be helpful in certain instances.
Sodium phosphate solution administered by mouth or by retention enema promotes calcium deposits in bone and inhibits its absorption from the GI tract.
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