Variation in liver function testing and the effect of pyridoxal-5-phosphate on ALT, AST and FIB-4 results

As one of the most requested profiles of blood tests, there is a need for standardization among liver function tests (LFT). Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are key markers of hepatocellular injury. ALT and AST are used to calculate a Fibrosis-4 (FIB-4) score for assessing liver fibrosis. Despite recommendations by the International Federation of Clinical Chemistry (IFCC) to include pyridoxal-5-phosphate in ALT and AST assay methodologies, most laboratories continue to omit this.

Data from the UK NEQAS for Clinical Chemistry Scheme, Distribution 1160 (November 2023), was reviewed to investigate variation in practice regarding liver blood tests in relation to ALT, AST and FIB-4. In addition, a series of questions audited laboratory practice in relation to liver enzymes.

Wide variation was seen in LFT profiles offered by laboratories, with 32 different combinations of tests used. The IFCC-recommended methods for ALT and AST are used by one-third of laboratories and give significantly higher results than non-IFCC methods. Laboratories using IFCC methods also reported significantly higher FIB-4 scores. Reference ranges and cut-offs for these tests also varied, and did not account for method-related differences in results.

The lack of standardization of LFTs can have a significant impact on patient care. The difference in results for ALT, AST and FIB-4 in laboratories not using IFCC-recommended methods may lead to misdiagnosis. This issue should be addressed by laboratories using methods including pyridoxal-5-phosphate. Until then, method-related reference ranges and cut-offs for ALT, AST and FIB-4 are required.