Hypercalcemia in Cats
Veterinary care should include diagnostic tests and subsequent treatment recommendations. Diagnostic tests must be performed to confirm the cause of hypercalcemia and exclude other diseases. The following diagnostic tests may be recommended: A complete history and physical examination. The history will include questions about changes in water consumption, urination, appetite, and weight and questions about reproductive status – whether your pet is sexually intact or neutered. Your veterinarian will also ask about previous illnesses, previous medications, exposure to rat poison or toxic plants. Physical examination will include palpation of the abdomen to evaluate for enlargement of the liver or spleen, palpation of the peripheral lymph nodes lying under the skin in various locations, and listening with a stethoscope to the chest to evaluate the heart and lungs.
A complete blood count (CBC), serum chemistry tests and urinalysis. An ionized calcium blood test also may be useful because the free (or ionized) calcium in the blood has important biological effects that contribute to the damaging effects of hypercalcemia in the body.
Your veterinarian may recommend additional diagnostic tests to exclude or diagnose other conditions or to better understand the impact of hypercalcemia. These tests insure optimal medical care and are selected on a case-by-case basis. Examples include:
Microscopic examination of lymph node samples collected by needle aspiration or biopsy
Microscopic examination of a bone marrow sample
Ionized calcium blood test to evaluate the biologically active form of calcium
Abdominal X-rays to evaluate for liver or spleen enlargement
Chest X-rays to evaluate for tumors or lymph node enlargement
Biopsy of any tumor masses found during physical examination
Ultrasound examination of the neck to evaluate the parathyroid glands and lymph nodes
Ultrasound examination of the chest to evaluate for tumors or enlarged lymph nodes
Ultrasound examination of the abdomen to evaluate for enlargement of lymph nodes, liver or spleen
X-rays of the skeleton to evaluate for tumors
Measurement of parathyroid hormone concentration in blood to evaluate for overactivity of the parathyroid glands
Adrenocorticotropic hormone (ACTH) stimulation test to evaluate the function of the adrenal glands and exclude the possibility of hypoadrenocorticism or Addison's disease
Measurement of the blood concentration of a substance called parthyroid hormone-related peptide (PTHrP) that serves as a marker of hypercalcemia caused by cancer
Blood concentration of vitamin D to evaluate for vitamin D intoxication
The decision to perform some diagnostic tests will be made based on the likelihood of specific disease processes. Your veterinarian will make these decisions on the basis of your cat's medical history and physical examination results. Some underlying disorders that may cause hypercalcemia and prompt your veterinarian to run specific tests include:
Lymphosarcoma. This malignancy is the most common cause of hypercalcemia in cats and diagnosis is based on a positive biopsy or cytology results obtained from enlarged lymph nodes, liver, spleen, kidney or bone marrow. X-rays of the chest and abdomen are often performed. Approximately 40 percent of cats with hypercalcemia caused by lymphosarcoma have a mass or enlarged lymph nodes in the chest that can be identified on X-rays.
Hypoadrenocorticism. Addison's disease may result in hypercalcemia in up to one-third of affected cats. The diagnosis is based on failure of the adrenal glands to respond to stimulation by the hormone adrenocorticotropin (ACTH).
Kidney failure. Affected cats also typically have high blood concentrations of phosphorus and waste products used to assess kidney function, including blood urea nitrogen (BUN) and serum creatinine. The kidneys can be damaged by persistent hypercalcemia, and sometimes it is difficult to determine if the kidney disease caused the hypercalcemia or the hypercalcemia caused the kidney disease.
Primary hyperparathyroidism. Overactivity of the parathyroid gland can cause marked hypercalcemia in cats that may have no symptoms other than increased water consumption and urination. Such cats usually have low or normal blood phosphorus concentrations, as opposed to those with kidney failure and hypercalcemia. The serum concentration of ionized calcium usually is high in affected cats. A high serum parathyroid hormone (PTH) concentration in a hypercalcemic cat supports a diagnosis of primary hyperparathyroidism. Ultrasound examination may allow identification of enlarged parathyroid glands. In normal cats, the parathyroid glands usually are not visible on ultrasound examination.
The parathyroid hormone-related peptide (PTHrP) test may identify cancer as the underlying cause of hypercalcemia.
Approximately 20 percent of cats with multiple myeloma, which is cancer of the antibody-producing plasma cells, have hypercalcemia, which may arise from the bone destruction caused by these tumors. The diagnosis is made by abnormal results of bone X-rays that appear as lucent or black areas in the normally white-appearing bony structure, a very high concentration of one specific blood protein (monoclonal gammopathy) identified on a serum protein electrophoresis test, increased numbers of antibody-producing plasma cells in the bone marrow, and fragments of the antibody protein molecules in the urine (Bence Jones proteins).
Vitamin D intoxication and hypercalcemia can be caused by consumption of vitamin D-containing rat poisons, vitamin D-containing plants (Cestrum diurnum, Solanum malacoxylon, Trisetum flavescens), or topical ointments containing a vitamin D-like chemical called calcitpotriene. Diagnosis is based on history of exposure. Blood concentration of vitamin D can be measured if necessary.