A-090 Comparison of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) Assays, with or without pyridoxal-5-phosphate, on various fibrosis scores

Abstract Background The most frequently ordered tests to assess hepatocellular injury are aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Conventional enzymatic methods for quantifying AST and ALT concentrations involve the transfer of an L-aspartate or L-alanine group, respectively, to 2-oxoglutarate. The coupled oxidation reaction with NADH is then measured spectrophotometrically at a wavelength of 340 nm. Pyridoxal-5-phosphate (PLP) is a cofactor for both ALT and AST and is necessary for their enzymatic activity. Conventional ALT and AST assays produced by most vendors do not include PLP. Thus, utilizing these assays in individuals with PLP deficiency may yield spurious results. The International Federation of Clinical Chemistry recommends adding PLP to the reaction to saturate the enzyme. Consequently, more vendors are reformulating their assays to include PLP. It is known that the addition of PLP leads to higher ALT and AST results. This assay modification and subsequent positive bias may have clinical implications, particularly in settings where liver function tests are used for non-invasive risk stratification of liver fibrosis. The aim of this study is to investigate the effect of utilizing ALT and AST results obtained from assays with and without PLP on non-invasive markers of fibrosis, including FibroScan, Fibrosis-4 (FIB-4) score, NAFLD fibrosis score (NFS), and the Aspartate Aminotransferase to Platelet Ratio Index (APRI). Methods Banked serum samples from outpatients on routine clinic visits were utilized for the study. Patients with clinical conditions such as hepatitis and liver diseases, which could potentially confound the results, were excluded. ALT and AST concentrations without PLP were measured using the Abbott Alinity conventional assay, while the Abbott activated assays were used to measure ALT and AST concentrations with PLP. Liver fibrosis risk stratification calculations were conducted using the FIB-4, NFS, and APRI scores. Other variables required for calculating the scores were obtained from patient charts. The two liver enzyme methods were compared using Deming regression analysis, Bland-Altman plots, and analysis of variance. Categorical variables were analyzed using the Chi-square test. Results A total of 259 patients (47% female, 53% male) were included in the study. The patients* ages ranged from 3 to 89 years, with a mean age of 55 years. The correlation coefficient for method comparison between assays with and without PLP was >0.99 for both ALT and AST, with biases of 16.6% and 13.3%, respectively. ALT and AST assays with PLP showed significantly higher concentrations than assays without PLP (P<0.05). Additionally, discrepancies were observed in liver fibrosis risk stratification, particularly in the FIB-4 score, with 12 discordant risk classifications between the two assays. However, no statistically significant differences were noted between the assays for NFS and APRI. Conclusion Our findings show that the Abbott ALT and AST assays with PLP yielded higher concentrations compared to the conventional Abbott Alinity assays without PLP, leading to discordant FIB-4 scores. However, no differences were observed for NFS and APRI scores. As liver blood tests increasingly contribute to non-invasive fibrosis assessment algorithms, clinicians and laboratorians need to evaluate the implications of assay reformulations on clinically relevant indices.

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