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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.


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 has 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 and 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.


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.


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.


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


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.



Brody, Tom. Nutritional Biochemistry. San Diego:Academic Press, 1998.

Key terms

Plasma — Plasma is blood with the cells removed.
Serum — Serum is blood plasma with the blood clotting proteins removed.


diminished levels of calcium in the blood; see table of Electrolyte Imbalances at electrolyte.


Abnormally low levels of calcium in the circulating blood; commonly denotes subnormal concentrations of calcium ions.


/hy·po·cal·ce·mia/ (hi″po-kal-se´me-ah) reduction of the blood calcium below normal.hypocalce´mic


An abnormally low concentration of calcium in the blood.


Etymology: Gk, hypo + L, calx, lime; Gk, haima, blood
a deficiency of calcium in the serum that may be caused by hypoparathyroidism, vitamin D deficiency, kidney failure, acute pancreatitis, or inadequate amounts of plasma magnesium and protein. Normal serum calcium levels range from 8.5 to 10.5 mg/dl. Mild hypocalcemia is asymptomatic. Severe hypocalcemia is characterized by cardiac arrhythmias and tetany with hyperparesthesia of the hands, feet, lips, and tongue. The underlying disorder is diagnosed and treated, and calcium is given by mouth or IV infusion. Hypocalcemia is also seen in dysmature newborns, in infants born of mothers with diabetes, or in normal babies of normal mothers delivered after a long or stressful labor and delivery. The condition is signaled by vomiting, twitching of extremities, poor muscle tone, high-pitched crying, and difficulty in breathing. Also spelled hypocalcaemia. See also Chvostek's sign, tetany. hypocalcemic, adj.


Calcium deficiency A condition characterized by ↓ Ca2+–< 2.1 mmol/L or 8.5 mg/dL Etiology ↓ ingestion or malabsorption of Ca2+, magnesium, or vitamin D, absent/ineffective PTH, acute renal failure, cancer, vitamin D-resistant rickets Clinical Neurologic and neuromuscular Sx–eg, irritability, depression, psychosis, muscle and laryngeal spasms, convulsions, arrhythmias, GI cramping, malabsorption. See Calcium; Cf Hypercalcemia.


Abnormally low levels of calcium in the circulating blood; commonly denotes subnormal concentrations of calcium ions.
Synonym(s): hypocalcaemia.


Abnormally low levels of calcium in the circulating blood.
Synonym(s): hypocalcaemia.


total serum calcium levels are lower than normal; both ionized calcium (physiologically active form) and nonionized calcium are depressed.

acute puerperal hypocalcemia
called also bovine parturient hypocalcemia; see milk fever.
bovine parturient hypocalcemia
see milk fever.
nonparetic parturient hypocalcemia
milk fever without recumbency in recently calved cows; inappetence, drop in milk production, alimentary tract stasis, reduced rumination; responds to treatment with parenteral injections of calcium solution.
non-parturient hypocalcemia
hypocalcemia, with or without clinical signs of staggery gait, recumbency, ruminal response which responds to treatment with parenteral calcium, occurring as incidents detached from parturient ruminants. A standard experience as mare eclampsia. In ruminants occurs as part of acute oxalate poisoning, sudden change to lush feed in heavily milking cows.
nutritional hypocalcemia
occurs most commonly in dogs and cats fed all-meat diets. See also all-meat syndrome.
ovine hypocalcemia
occurs at a high morbidity rate in lactating ewes subjected to bad weather or any other cause of reduced feed intake. The syndrome is similar to that in milk fever in cows, but occurs also in young sheep on meager rations, those grazing lush green cereal crops or pastures heavily contaminated by oxalate-bearing plants.
periparturient hypocalcemia
in ruminants hypocalcemia is most common in the immediate postparturient period due to the drain of lactation and inadequate parathyroid gland response and nutritional supply. In bitches and mares hypocalcemia occurs most commonly later in lactation. See also milk fever, lactation tetany (3), soluble oxalate poisoning, puerperal tetany.
renal hypocalcemia
chronic hypocalcemia due to chronic renal disease.
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