The increase of routine blood testing in pets is identifying increasing numbers of pets with elevated blood calcium levels, or hypercalcemia. Although this finding accompanies many medical abnormalities, there is a small group that shows no evidence of disease and their hypercalcemia is classified as idiopathic; or to put it simply, "we don’t know." For these pets nutritional intervention is an important part of the treatment program.
Calcium and Regulation
When most people think about calcium, they think about its role in bone structure. But precise blood calcium levels play an extremely important role for proper muscle and neurological function. Small changes of blood levels can have serious side effects on muscle contraction. Heart muscle is particularly sensitive so elevations or decreased levels can cause cardiac arrhythmias.
Channels on the membrane of cells require calcium to regulate the movement of chemicals in and out of cells. This is extremely important for the channels of nerve cells that regulate the movement of sodium and potassium for proper nerve function.
The tiny parathyroid glands that sit atop of the thyroid glands are responsible for the precise regulation of blood calcium levels. When blood levels of calcium decrease or the blood calcium-phosphorus ratio changes these glands secrete parathyroid hormone, or PTH, into the blood stream.
Elevated levels of PTH signals bone to release of calcium from the bone. PTH also signals the kidney to decrease calcium excretion and increase vitamin D activation. The activated vitamin D and PTH cause an increase in calcium absorption from the intestines. The combined effect of all of these events is to raise calcium blood levels.
Causes of Hypercalcemia
Overactive parathyroid glands or tumors of these glands results in an excessive secretion of PTH and hypercalcemia. Other types of tumors (like anal gland tumors in dogs) release a PTH-like hormone that works similarly to PTH elevated blood calcium levels. Diseases that cause bone deterioration, kidney failure, adrenal gland abnormalities, vitamin D toxicity (supplementation, plant, or rat poison ingestion), and aluminum toxicity can also cause hypercalcemia. Idiopathic hypercalcemia is a less common condition compared to those listed above.
Diagnosis of Idiopathic Hypercalcemia
An established diagnosis of idiopathic hypercalcemia is difficult. The first step is to rule out the more common causes. Blood tests, biopsies, X-rays, ultrasound, isotope scan,s and MRI may all be performed to identify parathyroid or adrenal gland abnormalities, tumors, kidney or bone abnormalities, and excessive vitamin D or other toxicities. Specific treatment of identified abnormalities will correct hypercalcemia. If no abnormalities are discovered, the diagnosis of idiopathic hypercalcemia is assumed. There is always caution with this diagnosis as early cancer or tumors may be small enough to avoid detection and glandular or organ dysfunction may not be progressed enough to provide definitive blood tests.
Nutritional Intervention for Hypercalcemia
Decreasing calcium ingestion and intestinal absorption are the main nutritional goals for pets with hypercalcemia. Commercial diets are not calcium or vitamin D restricted, so these pets typically require a balanced homemade diet with limited calcium and vitamin D supplementation. Organ meats like liver are not included in these diets as they are rich sources of vitamin A. Fish liver oils like cod are avoided as sources of omega-3 fatty acids as they are also rich in vitamin D. Care must be taken with these diets to ensure adequate levels of calcium and calcium-phosphorus ratios that do not initiate excessive PTH secretion from the parathyroid gland. Regular veterinary consultations and blood monitoring are necessary for pets on homemade diets to regulate their hypercalcemia.
Dr. Ken Tudor
Images: Main image from Carrboro Plaza Veterinary Clinic; image within text from Whitney Veterinary Hospital/Whitney Cat Care Clinic