Evaluation of the IFCC reference method for alanine aminotransferase: Spurious blank ALT activity due to contamination of D-alanine with L-alanine, and recommendations for a correction

Anthony Okorodudu, P. R. Pelletier, A. A. Valcour, G. N. Bowers, R. B. McComb

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During an evaluation of the IFCC reference method for alanine aminotransferase (ALT, EC, we noted that the specimen blank activity reaction was markedly increased. Experience with five different lots of D-alanine from four commercial sources indicated that substantial and varying negative bias (up to -10%) could be introduced into the blank-corrected ALT activity, depending on the lot of D-alanine used. Although the IFCC procedure for ALT mentions the possibility of this L-alanine contamination, we believe that the degree of contamination in commercial reagents is underestimated. Analyzing the five lots of D-alanine for L-alanine, we found the magnitude of negative bias to be correlated directly with L-alanine contamination. Here, we describe a quick, sensitive assay based on coupled reactions of L-amino acid oxidase/peroxidase for quantifying L-alanine in the concentration range of 0-15 mmol/L without a sample-dilution step. Results by this alternative L-alanine assay agreed well with those recommended in the IFCC ALT procedure. Further examination suggested an even simpler solution to the L-alanine contamination problem, because we found no difference in the blank-corrected ALT activity determined in Tris HCl buffer, with or without D-alanine (free of L-alanine). We therefore propose that D-alanine be omitted from the IFCC reference ALT procedure.

Original languageEnglish (US)
Pages (from-to)153-156
Number of pages4
JournalClinical Chemistry
Issue number1
StatePublished - 1989
Externally publishedYes


ASJC Scopus subject areas

  • Clinical Biochemistry

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