Veterinary Medicine - July 2008 - (Page 393)

TABLE 1 TABLE 2 Clinical Signs Associated with Feline Hypercalcemia Lethargy, depression Anorexia Vomiting Changes in urination Abdominal pain Increased thirst Constipation Ataxia Twitching Causes of Hypercalcemia: GOSH DARN IT G O S H D A R N I T Granulomatous disease (fungal, parasitic, bacterial) Osteolytic disease (tumor, infection) Spurious (laboratory error, lipemia, hemolysis) Hyperparathyroidism Drug related (thiazide diuretics, calcium-containing phosphate binders) Addison’s disease (hypoadrenocorticism) Renal failure (acute, chronic) Nutritional (excess vitamin D, vitamin A, or calcium) Idiopathic Tumors with elevated tCa concentrations, with tCa concentrations at the upper end of the normal range, or exhibiting risk factors associated with hypercalcemia (e.g. calcium oxalate urolithiasis, chronic renal failure).2 Several commercially available in-house machines can accurately measure iCa concentrations, or a reference laboratory may be used. Samples must be collected anaerobically, handled correctly, and shipped appropriately, as changes in pH can substantially alter the percentage of calcium bound to protein and, thus, the iCa concentration. Total calcium concentrations can be spuriously elevated. Lipemia and hemolysis can affect colorimetric measurements. Before considering additional diagnostic tests, always verify hypercalcemia, either by repeating a tCa measurement in a fasted patient or by determining the iCa concentration. SIGNS OF HYPERCALCEMIA Cats appear to be more resistant to the clinical consequences of hypercalcemia than are dogs, and it is not unusual to document substantial hypercalcemia in an apparently normal patient.2 The most prevalent clinical signs reported in hypercalcemic cats are vague and nonspeci c, such as lethargy, depression, and anorexia.2 Other changes include an increase in thirst and urination due to antidiuretic hormone antagonism at the renal collecting ducts, or dysuria and abdominal pain secondary to calciumcontaining uroliths (Table 1). As serum calcium concentrations continue to rise, gastrointestinal disturbances (vomiting and constipation) or neuromuscular dysfunction (twitching and seizures) may be noted. If the serum calcium-phosphorus product exceeds 70, tissue mineralization and secondary organ damage—primarily renal—are expected. Precipitous increases in serum calcium concentrations are often fatal.2 CAUSES OF HYPERCALCEMIA 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 modi cation 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 de ned 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 identi ed were neoplasia (n = 21), renal failure (n = 18), VETERINARY MEDICINE July 2008 ESSENTIAL ELEMENTS • Always verify hypercalcemia with a repeat total calcium (tCa) or ionized calcium (iCa) concentration measurement. • An elevated iCa concentration deﬁnes true hypercalcemia. • Measure the iCa concentration in any cat with a tCa concentration at or above the upper end of the reference range. • Measure the iCa concentration in any cat with renal failure or calcium oxalate urolithiasis, even if its tCa concentration is normal. • Severe hypercalcemia mandates immediate attention, and therapy to reduce the serum calcium concentration may be necessary while further diagnostic tests are performed. • Most causes of feline hypercalcemia can be diagnosed with a straightforward work-up. • Idiopathic hypercalcemia can only be diagnosed after all other causes have been excluded. 393

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Veterinary Medicine - July 2008 Contents Leading Off Practical Matters Idea Exchange Clarification Dental Corner The Diagnostic Approach to Hematuria Guidelines for Evaluating Hypercalcemic Cats CE Form Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - July 2008

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