Cats with hypercalcemia exhibit clinical signs less frequently than dogs do. However, with this article's helpful mnemonics for recalling the causes of feline hypercalcemia and a diagnostic algorithm, you will be prepared to provide the best care for your feline patients.
In general, hypercalcemia reflects increased gastrointestinal uptake or increased calcium release from bone; decreased renal
calcium excretion is rarely the cause. Mnemonics have been devised to help you remember all the causes of hypercalcemia. For
example, Table 2 is a modification of the GOSH DARN IT list.
The most comprehensive recent case series of feline hypercalcemia was published in 2000.1 This retrospective study evaluated 71 cats and defined hypercalcemia on the basis of tCa concentrations > 11 mg/dl (reference
range = 9.2 to 10.2 mg/dl). The authors reported that the most common disorders identified were neoplasia (n = 21), renal
failure (n = 18), urolithiasis (n = 11), and primary hyperparathyroidism (n = 4). However, iCa concentrations were not measured,
so some of these may not have been true feline hypercalcemia cases. In fact, many cats with chronic kidney disease have normal
iCa concentrations and, thus, are not truly hypercalcemic.4
Cats with neoplasia had higher serum calcium concentrations (13.5 ± 2.5 mg/dl) than cats with renal failure did (11.5 ± 0.5
mg/dl).1 Eight of the 11 cats with urolithiasis had calcium oxalate stones confirmed at surgery.1 An underlying cause of hypercalcemia was not identified in any of the cats with urolithiasis. Based on the exclusion of
other recognized causes, these patients fit the criteria for idiopathic hypercalcemia.5 This term was first proposed in the late 1990s and is now applied to any cat with unexplained, repeatable hypercalcemia.
Since it is a diagnosis of exclusion, every reasonable effort must be made to rule out other likely causes.
The SHIRT list (Table 3) is a mnemonic devised to help you remember the common causes of feline hypercalcemia. Table 4 summarizes the classic serum chemistry profile findings in cats with the commonly identified causes of hypercalcemia and
demonstrates the parameters expected in idiopathic cases.