Abstract
Blood specimens from the retro-orbital sinus of 80 Sprague Dawley rats were collected into tubes containing lithium heparin either as a solid or an aqueous solution. Plasma was separated for blood chemistry analysis. Twenty-eight blood specimens collected into tubes containing solid heparin were clotted and eight specimens were partially clotted making these samples unsuitable for some analyses. None of the specimens collected into heparin solution showed any evidence of clotting. The variances of lactate dehydrogenase and α-hydroxybutyrate dehydrogenase activities in plasma prepared with solid heparin were significantly greater than those prepared with heparin solution. Lithium heparin solution is now used routinely in our laboratory.