Tests & Diagnosis

After your cat has been documented with a high serum Total Calcium (tCa) concentration, this test includes ionized calcium, complex calcium, and protein-bound calcium, a test for serum Ionized Calcium (iCa) concentration is required. If the result is normal, the patient is not truly hypercalcemic.

Hypercalcemia Serum Values
tCa > 10 mg/dL
iCa > 5.5 mg/dL or
iCa > 1.4 mmol/L
Mild HC
Moderate HC
Severe HC
tCa < 13 mg/dL
tCa 13 - 15 mg/dL
tCa > 15 mg/dL
these numbers are for a general idea of hypercalcemic values
results may vary due to differences in laboratory reference ranges

If the iCa is increased, a urinalysis (for evidence of protein, calcium oxalate stones and decreased specific gravity) and serum chemistry profile for renal (kidney) function is evaluated. iCa is affected by exposure to oxygen and pH, so serum samples are collected anaerobically. The sample must also be of a non-lipemic (non-fatty), non-hemolyzed (non-destructed) serum or the results may be skewed. Certain soaps used in the laboratory may also affect the test, so care must be taken in the handling and cleaning of laboratory glassware and equipment that will be utilized for the test. Dehydration is a common clinical situation that can result in mildly increased blood calcium concentration. Blood calcium concentration should be re-evaluated after the patient has been rehydrated by intravenous or subcutaneous (under the skin) administration of fluids.

FeLV (Feline Leukemia Virus) and/or FIV (Feline Immunodeficiency Virus) tests may also be administered in patients with uncertain retroviral status.

Physical examination should prove to be unremarkable but sometimes either through physical examination or radiography, the kidneys in some affected cats are noted as smaller than normal.

If it is possible that your cat was exposed to rat poison, a test for Vitamin D concentration is advocated. Calciferols (Vitamin D) are a type of rodenticide. These compounds work by affecting the levels of Vitamin D and calcium in the body. Ingesting Vitamin D in toxic doses causes hypercalcemia. This is a condition where the calcium level is raised to such a degree that the stomach, kidneys, lungs, blood vessels and heart are all damaged by calcification. If the Vitamin D concentration is normal further tests are warranted.

The serum phosphorus should also be checked as the calcium phosphorus ratio is extremely important in maintaining a healthy feline body. The calcium phosphorus ratio is usually defined as 1.3 : 1 respectively. In rodenticide poisoning, cats often exhibit both high Vitamin D levels (hypervitaminosis D) and high phosphate levels (hyperphosphatemia).

Tests must now be done to determine if your cat has primary hyperparathyroidism (excessive secretion of parathyroid hormone resulting in abnormally high levels of calcium in the blood; can affect many systems of the body, especially causing bone resorption and osteoporosis) or neoplasia (the pathological process that results in the formation and growth of a tumor).

PTH concentration (parathyroid hormone) is low normal and the PTH-rP concentration (parathyroid hormone related protein) is low or undetectable in cats with Idiopathic Hypercalcemia.

Finally, radiographs may be taken of the thorax and/or abdomen to search for neoplasia. If no abnormalities are identified your veterinarian will diagnose your cat with Idiopathic Hypercalcemia (IHC).


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