Effects of Pyridoxal-5'-Phosphate on Aminotransferase Activity Assay

ABSTRACT

BACKGROUND: Pyridoxal-5'-phosphate (P5P), a coenzyme of the aspartate aminotransferase (AST) and alanine aminotransferase (ALT) reactions, is required to measure aminotransferase levels (IFCC method). However, a modified IFCC method that uses a reagent devoid of P5P is commonly used in laboratories in Korea. To determine the differences between the two methods, we compared aminotransferase levels measured by using the IFCC method and modified IFCC method. METHODS: Serum levels of AST and ALT, with and without P5P, were measured in 2,318 patients. Based on the allowable limits of performance set by the Royal College of Pathologists of Australasia (RCPA), differences between the two methods were analyzed under various conditions. RESULTS: Higher AST and ALT values were obtained by the IFCC method compared to modified IFCC method, showing significant differences between the two methods (AST, 5.8±14.2 IU/L; ALT, 2.8±6.9 IU/L) (P<0.001). Values exceeding RCPA criteria were more frequently observed in emergency orders (AST, 65.8%; ALT, 14.4%) than in routine orders (AST, 3.2%; ALT, 9.6%), as well as in inpatient wards (AST, 70.4%; ALT, 18.5%) compared to outpatient clinics (AST, 56.6%; ALT, 10.0%). However, the differences between the two methods were not significant among the disease groups, except for the acute myocardial infarction group. CONCLUSIONS: The method using reagents without P5P underestimated aminotransferase activity. The effect of P5P was more significant in patients with acute myocardial infarction, considered as P5P-deficient. In conclusion, the IFCC method with P5P should be applied for measuring AST and ALT serum levels.