hypocalcemia

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 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.

— Tom Brody, PhD

An abnormally low concentration of calcium in the blood; may be associated with hypoparathyroidism, rickets, osteomalacia, renal rickets, pancreatic disease, sprue, obstructive jaundice, or tetany.

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

• acute puerperal h. — called also bovine parturient hypocalcemia; see milk fever.
• bovine parturient h. — see milk fever.
• nonparetic parturient h. — 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 h. — 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 h. — occurs most commonly in dogs and cats fed all-meat diets. See also all-meat syndrome.
• ovine h. — 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 h. — 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 h. — chronic hypocalcemia due to chronic renal disease.