Feline (cat) hemolytic complement optimal testing conditions.

Optimal conditions for assaying feline (cat) hemolytic complement (C) were determined. Effects of the following factors on C titers were tested: pH, ionic strength; calcium, magnesium, and ethylenediamine tetraacetate concentrations; time and temperature of incubation. Guinea pig erythrocytes sensitized with feline antibody were the most sensitive target cells for feline C. A buffer of pH 7.3, with an ionic strength of 0.06 and containing 0.3 mM CaCl2 and 1 mM MgCl2, was optimal for feline C assay. A concentration of 4 mM ethylenediamine tetraacetate in calcium- and magnesium-free buffer inhibited the C reactivity to 1/53rd of the original titer. Sera from clinically healthy cats contained 70 to 150 CH50 (50% hemolytic) U/ml when tested, using 1 x 10(8) sensitized guinea pig erythrocytes/ml.