Hypocalcemia (Low Calcium Levels) in Cats

By Malcolm Weir, DVM, MSc, MPH; Ernest Ward, DVM

What is calcium and why is it important?

Calcium is a mineral that is found in small quantities throughout the body. It plays an important role in such varied and vital functions as muscle contraction, transmission of nerve impulses, blood clotting, and bone growth.

What is hypocalcemia?

Hypocalcemia means that the level of calcium in the bloodstream is low. Regulation of the calcium concentrations in the blood is sometimes impaired and may result in low blood calcium concentrations.

What are the clinical signs of hypocalcemia?

Mild decreases in blood calcium concentrations will not usually result in any clinical signs, but may be detected on routine blood testing. However, if moderate to severe hypocalcemia develops, then clinical signs may occur.

Early signs of hypocalcemia include restlessness, stiffness, weakness, irritability, muscle tremors and hypersensitivity (exaggerated responsiveness) to touch and sound. More profound signs include severe generalized muscle twitching, leading on to uncontrolled muscle spasms, seizures, and ultimately death.

What causes hypocalcemia?

In the cat, chronic renal failure (CRF) (also called chronic kidney disease [CKD]) is the most common cause of hypocalcemia. Azotemia (elevated levels of the two kidney enzymes: BUN and creatinine in the blood) and hyperphosphatemia (elevated blood phosphorus levels) result from decreased kidney filtration and function. Calcium and phosphorus levels are closely inter-related and when phosphorus levels increase, calcium levels decrease.

When calcium levels decline, the parathyroid gland will enlarge and secrete additional parathyroid hormone (PTH) in an effort to maintain serum calcium in the normal range. The hypocalcemia caused by chronic renal failure, however, is rarely clinically significant (i.e., muscle tremors, twitches, tetany, or convulsions do not develop). Fortunately, most pets with chronic renal failure have normal serum calcium concentrations. With hypocalcemia due to chronic renal failure, treatment is directed at lowering the serum phosphate concentrations by dietary restriction of phosphorus and administration of intestinal phosphate binders.

"Hypocalcemia may occur as a post-operative complication
following surgical treatment for hyperthyroidism."

In cats, hypocalcemia may occur as a post-operative complication following surgical treatment for hyperthyroidism (a common condition in older cats). When a thyroidectomy, or surgical removal of the thyroid gland, is performed, the parathyroid gland, located near the thyroid gland, may be inadvertently damaged or removed. This results in a condition known as hypoparathyroidism or low parathyroid hormone, which causes low blood calcium and high blood phosphorous concentrations. Because of this risk, cats may be hospitalized for several days after a thyroidectomy so that blood calcium concentrations can be monitored and treatment given if necessary.

There are other, less common causes of hypocalcemia, including hypocalcemia associated with lactation in a nursing mother (known as puerperal tetany, eclampsia, or milk fever), low blood protein levels (hypoproteinemia), pancreatitis, and certain drugs and toxins.

How is hypocalcemia treated?

If the hypocalcemia is severe, immediate correction of the decreased levels will require calcium injections. Most cats with severe hypocalcemia will need to be hospitalized until calcium levels stabilize, as this condition is potentially life threatening.

Long-term treatment of hypocalcemia may include supplementing the diet with calcium salts, and administration of vitamin D (tablets, capsules, or liquid), which is used to increase the absorption of calcium from the intestinal tract. Regular monitoring of blood calcium concentrations will be needed by your veterinarian to ensure successful treatment. The duration of treatment depends on the underlying cause of the condition.

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