Validity of testing alanine aminotransferase in refrigerated whole blood

Alanine aminotransferase (ALT) was tested in the sera and plasma of in-line segments as well as the main bags of whole blood units collected from blood donors. The purpose of this study was to evaluate the stability of enzyme activity during blood storage when the analysis of ALT is postponed over weekends or holidays. In addition, when validation of a particular result is requested, an in-line segment may be convenient for confirmatory testing. While a dilutional effect was found, the anticoagulant in the main collection bag was not shown to have affected enzyme activity. During storage the mean enzyme concentration decreased. Appropriate plasma ALT cutoffs for respective time periods during storage were calculated to compensate for downward drift. This correction prevented the use of the blood units (40% of total) that would erroneously have appeared transfusable if the serum cutoff had been used. If the Day 0 plasma cutoff was used throughout the total storage time period, 14 percent of the blood would erroneously have appeared transfusable.