[Ionized calcium and total calcium in the cat].

The concentrations of total calcium (Catot), of the biologically active ionized calcium fraction (Caion), and of albumin were measured from the plasma of 92 healthy cats and 154 patients. Only a moderate correlation existed between the concentrations of Catot and Caion (r = 0.718), so that the concentration of Catot reflects the calcium homeostasis only to a limited extent. An essential reason for this lies in the distinct dependence of the Catot on the albumin concentration (r = 0.628). On the basis of the 2.5 and 97.5% quantile of the healthy cats, the reference range for Caion was 1.15-1.37 mmol/l (age group > or = 6 months, < 2 years: 1.23-1.38; > or = 2 years: 1.14-1.35 mmol/l), for Catot 2.49-2.87 mmol/l (2.52-2.92; 2.35-2.81 mmol/l) and the fraction of Caion of the Catot 44.5-50.6%. Like the Catot, the Caion also showed no dependence on the sex. Against that, the distinct dependence on age of these two parameters (p < 0.001), which expresses the decreasing Ca concentration in older animals, should be regarded for a discriminating interpretation of measurement results.