Biological variability in aspartate aminotransferase activity in serum of healthy persons, and effect of in vitro supplemantation with pyridoxal 5-phosphate.

Aspartate aminotransferase (EC 2.6.1.1) activities in sera from nine healthy individuals were monitored during two weeks, both with and without first supplementing the serum with pyridoxal phosphate. Pyridoxal phosphate supplementation caused a mean increase of 39% (range, 33-55%) in measured activity. The biological variability during the two-week period was independent of pyridoxal phosphate supplemantation. The intra-individual variability (CV) was 5.3% and 5.1% with and without pyridoxal phosphate supplementation, respectively; the corresponding inter-individual variability was 13.2% and 13.6%. We conclude that the reference interval will be insensitive to intra-individual fluctuations in aspartate aminotransferase activity in serum, whether or not the serum is supplemented with pyridoxal phosphate.