Importance of pyridoxal-5'-phosphate addition to the assay medium for the measurement of catalytic concentrations of plasma aspartate and alanine aminotransferases in patients undergoing antineoplastic chemotherapy

Using 98 plasma samples from cancer patients undergoing antineoplastic chemotherapy, we compared the activities of aspartate aminotransferase and alanine aminotransferase measured by two different methods, with and without the addition of pyridoxal-5'-phosphate to the assay medium. Pyridoxal-5'-phosphate caused an increase of 1 to 20 U/l in aspartate aminotransferase and alanine aminotransferase activity in 90 and 78 patient plasma samples, respectively. Increases of aspartate aminotransferase and alanine aminotransferase activity of more than 20 U/l were observed in 8 and 20 samples, respectively. In 8 cases, the increase in alanine aminotransferase activity was greater than 50 U/l, whereas a similar increase in aspartate aminotransferase activity was detected in only 2 cases. The considerable pyridoxal-5'-phosphate activation in aminotransferase activity observed in the plasma of a significant number of patients suggests that the use of the method with pyridoxal-5'-phosphate is advisable for a correct measurement of the catalytic concentration of aminotransferases in the plasma of patients undergoing chemotherapy.