The purpose of this study was to compare whole blood and plasma in terms of the subsequent accuracy of blood lactate, glucose, lactate dehydrogenase (LDH), creatine phosphokinase (CPK), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) measurement. Blood samples were drawn from 8 male Wistar-Kyoto rats. The rats were homologous, weighed 300- 380 g, were housed in the same environment, and were provided with food and water under the same conditions. Blood draws occurred in all rats at same time. The blood specimens were divided into two samples, one to be stored as whole blood (WBS) and one to be stored as plasma (PS). All the blood sample analyses were performed by trained and experienced personnel to ensure that differences in results were due to variation in form in which specimens were stored rather than to technique. The lactate concentration in the WBS group gradually increased over time, intraclass correlation coefficient (ICC) = 0.541, 95% confidence interval (CI; -0.197, 0.893), and was higher than that of the PS group, ICC = 0.897, 95% CI (0.733, 0.976). By contrast, glucose level gradually declined for the WBS group, ICC= -0.367, 95% CI (-2.563, 0.682). Whole blood storage increased measurement variation for lactate, glucose, LDH, and CPK. Plasma storage prolonged the stability of the biochemical components. This study demonstrates the importance of evaluating validity at each stage of developing and testing animal models.