A comparison of serum ionized calcium concentrations and serum total calcium concentrations in dogs with lymphoma

Serum ionized calcium and total calcium concentrations were measured in 16 dogs with lymphoma and 49 healthy control dogs. Blood samples for all determinations of ionized calcium were collected into tubes containing silicone separator gel and processed under a closed anaerobic system. An ionized calcium analyser with ion selective electrodes was used to determine pH, ionized calcium and ionized calcium adjusted to pH 7.4. Reference ranges for ionized calcium (iCa pH 7.4) of 1.30-1.46 mmol/l, and for total calcium of 2.37-2.82 mmol/l were established. A stronger correlation (r = 0.85) was found between measured ionized calcium and total calcium levels in dogs with lymphoma and hypercalcaemia than in those with lymphoma and normocalcaemia (r = 0.64). Measurement of serum ionized calcium was diagnostically concordant with the measurement of serum total calcium in the determination of calcium status in all dogs with lymphoma. Serum ionized calcium did not provide a diagnostic advantage over total calcium in the detection of hypercalcaemia of malignancy in these dogs.