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Hypocalcemia is defined as a blood ionized calcium (iCa) level < 6.5 mg/dL (< 1.25 mmol/L) (normal 9 - 11.4 mg/dL).

Serum total calcium does not accurately predict ionized calcium status in many clinical conditions[1]. Calcium homeostasis in hypoalbuminemic critically ill dogs should be evaluated by iCa concentrations rather than total calcium or calcium adjusted for albumin or total protein[2].

Calcium is a vital intracellular and extracellular ion involved in neuronal activation, muscle contraction, enzymatic reactions, hormone secretion, and bone matrix.

Normal calcium homeostatic mechanisms maintain extracellular calcium concentrations within a narrow normal range and changes often result in abnormal skeletal and cardiac muscle activity.

Extracellular calcium exists in three forms: ionized (the biologically active form), complexed (to plasma buffers), and protein-bound (mainly to albumin). Most commonly, total calcium is measured on serum biochemical analyses and represents the sum of all calcium fractions. Serum-ionized calcium (iCa) concentration is a more accurate measure of hypercalcemia than total serum calcium or corrected serum calcium concentrations[3].

In dogs with hypocalcemia, the low concentration of calcium causes an excitatory effect on nerve and muscle cells, lowering the threshold potential and discharging repetitively without provocation. Tetany occurs as a result of spontaneous repetitive firing of motor nerve fibers.

Hypoglycemia can occur concurrently in dogs.

Although commonly observed in young dogs associated with inadequate dietary calcium, a number of disease may also cause hypocalcemia, including:

Dogs with hypocalcemia may be clinically normal, but sever hypocalcemia may cause shivering, muscle fasciculation and seizures[15].

In dogs with nutritional secondary hyperparathyroidism, clinically affected dogs often present with joint pain due to osteopenia, which can be confirmed on radiographs[16].

Treatment involves addressing the acute hypocalcemia with parenteral calcium gluconate (10 mL of 10% calcium gluconate in 250 mL of 0.9% saline administered at 2.5 mL/kg/hr for 8 – 12 hours).

Severe and persistent hypocalcemia is associated with ventricular tachyarrhythmias and fibrillation, leading to sudden death[17].


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  17. Ricco ML et al (2009) Effects of hypocalcemia on electrical restitution and ventricular fibrillation. Conf Proc IEEE Eng Med Biol Soc 2009:4182-4185