Intermethod calibration of alanine aminotransferase (ALT) and γ-glutamyltransferase (GGT) results:: application to Fibrotest® and Actitest® scores

Two multi-component scores ( Fibrotest (R) and Actitest (R)) have been proposed to evaluate liver fibrosis or necro-inflammatory lesions as an alternative to liver biopsy. This approach requires standardization of alanine aminotransferase ( ALT) and gamma-glutamyltransferase ( GGT) determinations. For this purpose, ALT and GGT values were assigned to a multi-enzyme material using the appropriate primary reference procedure. This material was used as a common calibrator for sera from 20 patients with viral hepatitis. Measurements were carried out in 11 laboratories, using their own automated routine methods and compared to results obtained using the primary reference procedure. The expression of results in multiples of the upper reference limit worsened the inter-laboratory variation for both enzymes. The multi-enzyme material was commutable for ALT and GGT determination carried out with six analytical systems. Common calibration significantly improved inter-laboratory consistency, which finally reached 1.8% and 3.3% for ALT and GGT, respectively. For each enzyme, it also permitted the retention of a common reference interval for a set of calibrated methods and the improvement of inter-laboratory coherency of Fibrotest (R) and Actitest (R) scores.