Improved alanine aminotransferase assay using the microtiter plate.

New procedures and new devices have been developed to improve the alanine aminotransferase (ALT) assay by using microtiter plates with 96 wells. Sera for ALT determination and reagents are distributed with a computer-controlled multiple syringe for simultaneous filling of the 96 wells. The volumes simultaneously distributed by this new multiple syringe show very little variation. The coefficient of variation (CV) is 0.6 percent (n = 96). Repeated filling of the wells with this syringe results in good reproducibility of distributed volumes (CV = 0.5%, n = 10). The temperature of sera, reagents, and mixtures, even during photometry, is actively regulated (down or up) to 25 degrees C in special chambers. Thus, the temperature varies minimally +/- 0.05 degrees C. ALT values in the low normal range as well as the high pathologic range show little variation (CV less than 2.3%) in aliquots of the same sample simultaneously or subsequently examined by the new procedure and with new devices. There is good correlation between the improved method using microtiter plates and the conventional methods (r greater than 0.9900, ALT values from 1-154 U/L). False-low and false-high values are excluded by computerized evaluation of many single determinations during the kinetic reactions in each sample. The new method is precise as well as simple, saves time, and may become important for the determination of other serum constituents on the basis of kinetics.