IONIZED CALCIUM AND TOTAL CALCIUM IN THE CAT

The concentrations of total calcium (Ca-tot), of the biologically acti ve ionized calcium fraction (Ca-ion, and of albumin were measured from the plasma of 92 healthy cats and 154 patients. Only a moderate corre lation existed between the concentrations of Ca-tot and Ca-ion (r = 0. 718), so that the concentration of Ca-tot reflects the calcium homeost asis only to a limited extent. An essential reason for this lies in th e distinct dependence of the Ca-tot on the albumin concentration (r = 0.628). On the basis of the 2.5 and 97.5% quantil of the healthy cats, the reference range for Ca-ion was 1.15-1.37 mmol/l (age group greate r than or equal to 6 months, < 2 years: 1.23-1.38; greater than or equ al to 2 years: 1.14-1.35 mmol/l), for Ca-tot 2.49-2.87 mmol/l (2.52-2. 92; 2.35-2.81 mmol/l and the fraction of Ca-ion Of the Ca-tot 44.5-50. 6%. Like the Ca-tot, the Ca-ion 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 a nimals, should be regarded for a discriminating interpretation of meas urement results.