Hypocalcemia in small animals is a total serum calcium concentration in animals less than 6 months old is <9 mg/dL in dogs or <7 mg/dL in cats. It is best to measure the concentration of ionized calcium, which is the biologically active form, rather than total calcium. Ionized calcium concentration should be in the range of 1.25–1.45 mmol/L. Hypocalcemia exists when the ionized calcium concentration is <1 mmol/L. Clinicians should always consider reference ranges for individual laboratories and patient clinical signs.
Etiology of Hypocalcemia in Small Animals
Serum calcium concentration may be affected by laboratory error (lipemia), acid-base status (alkalosis decreases ionized calcium, and acidosis increases ionized calcium), and plasma protein concentration. Hypoalbuminemia decreases total serum calcium, although ionized calcium concentration is not affected. Hypocalcemia is an important electrolyte disturbance in critically ill dogs and cats.
Common causes of hypocalcemia include:
hypoparathyroidism, including iatrogenic hypoparathyroidism (postthyroidectomy)
acute renal failure
chronic renal failure
acute pancreatitis
hypoalbuminemia
eclampsia (puerperal tetany )
intestinal malabsorption
toxins, drugs (eg, ethylene glycol, piperazine, phosphate enemas)
nutritional secondary hyperparathyroidism
hyperadrenocorticism
Hypocalcemia, hypovitaminosis D, and metabolic acidosis occur in dogs with induced endotoxemia. Feeding lipopolysaccharides may mediate a decrease in vitamin D–binding protein, with subsequent loss of vitamin D in the urine. In addition, dogs with blunt and penetrating traumatic injuries, particularly abdominal trauma, are substantially more likely to have hypocalcemia (low ionized calcium concentration). These dogs spend more time in the hospital and ICU, require more intensive treatments, and are less likely to survive than dogs with normocalcemia. Hypocalcemia due to critical illness or traumatic injury can cause clinical signs similar to those of eclampsia (eg, hyperexcitability, including tremors, twitching, spasms, or seizures); or more subtle signs related to cardiovascular collapse).
Clinical Findings of Hypocalcemia in Small Animals
Clinical signs of hypocalcemia vary from none to nonspecific anorexia, facial rubbing, growling, nervousness, focal muscle twitching (ear and face), and stiff gait, to severe neuromuscular dysfunction with tetany and seizures. Exercise and excitement may induce or worsen clinical findings. The severity of clinical signs depends on the magnitude of hypocalcemia, rapidity of onset, and duration.
Diagnosis of Hypocalcemia in Small Animals
Diagnosis of hypocalcemia is usually based on the history, physical examination findings and results of serum biochemical testing including serum lipase concentration, and a urinalysis. An ionized calcium concentration of <1 mmol/L is diagnostic for hypocalcemia.
Treatment and Prevention of Hypocalcemia in Small Animals
Treatment of hypocalcemia is aimed at correcting the underlying disorder. If clinical signs are present, vitamin D, supplementation, calcium supplementation or both are indicated, as for eclampsia. Treatment is also indicated if serum total calcium is <7.5 mg/dL or ionized calcium is <0.8 mmol/L.
