Stability of Aspartate Transaminase in Blood Specimens Subjected to Various Storage Temperatures and Times Prior to Centrifugation

Aspartate Transaminase (AST) is an enzyme used to diagnose medical problems and found in erythrocytes other than in the heart, liver, skeletal muscles, kidney, and brain. Prolonged serum-clot contact time and the fluctuation in storage temperature are possible reasons for the changes in chemical constituents in serum. The objective of this experimental study was to determine the effect of the storage time (three and six hours) before centrifugation and the storage temperature (4℃ and 28℃) on the stability of AST in blood. Methods: The study sample consisted of fifty-three healthy adult volunteers. Five milliliters of blood samples were collected from each subject and then aliquoted into five Eppendorf tubes. One of the aliquots was centrifuged within 30 minutes of collection, and the AST assay was done to obtain the control (baseline) value. Two of the remaining aliquots were stored at 4℃ while the other two aliquots were stored at room temperature for three hours and six hours, respectively prior to centrifugation. The difference between the baseline AST values and paired values of samples at different times of storage and temperatures was analyzed using the non-parametric Wilcoxon signed-rank test. Results: Significant differences were found in AST level compared to the baseline value when samples were stored at room temperature for three hours (p=0.027) and six hours at room temperature (p=0.011). Conclusions: AST in blood was unstable for at least three hours at room temperature (28℃). At 4℃, AST was stable for up to six hours, and blood samples can be stored at 4℃ for up to six hours for analysis of AST.