Effect of storage on measurement of ionized calcium and acid-base variables in equine, bovine, ovine, and canine venous blood.

The stability of blood ionized calcium (Ca2+) and acid-base variables in equine, bovine, ovine, and canine venous blood samples (n = 15, in each group) stored at 4 C for 3, 6, 9, 24, or 48 hours was studied. Variables included blood Ca2+ and standard ionized calcium (Ca2+ corrected to pH 7.4) concentrations, pH, blood carbon dioxide and oxygen tensions, base excess, bicarbonate concentration, and total carbon dioxide content. Results indicate that storage of blood samples at 4 C for up to 48 hours, despite appreciable acid-base changes, is associated with less than 1.5% change in equine, bovine, and ovine blood Ca2+ concentrations. Similar changes were observed in canine blood during the first 9 hours' storage. After 24 and 48 hours' storage, clinically relevant decrease (10.5 and 15.5%) in canine blood Ca2+ concentration was measured. Therefore, Ca2+ concentration in equine, bovine, and ovine venous blood samples stored up to 48 hours, and in canine blood samples stored up to 9 hours at 4 C is of diagnostic use.