We read with great interest the article by Joka et al.,1 who demonstrated that, compared with the widely used apoptosis marker M30, the M65 assay had a better diagnostic performance and even differentiated between lower fibrosis stages as well as between healthy individuals and patients with simple steatosis. However, there are some issues in terms of data analysis and interpretation that merit consideration.
First, the authors claimed that, unlike the M30 assay, only serum levels of total M65 significantly discriminated between patients with nonalcoholic fatty liver disease (NAFLD) and healthy controls.1 However, this finding is not surprising given the very small number of patients with simple steatosis (n = 10) and nonalcoholic steatohepatitis (n = 12) enrolled in this study. Actually, the results concerning M30 may be just a false-negative finding due to the fact that the study was underpowered for such a comparison. Indeed, we have shown that among patients with NAFLD, M30 and M65 distinguished between advanced fibrosis and early stage fibrosis with a similar sensitivity and specificity.2 Second, the authors used Ishak fibrosis stage in all patients with chronic liver disease, regardless of the underlying etiology.1 One may argue whether the application of a disease-specific score for fibrosis (such as the METAVIR score3 for HCV fibrosis or the Kleiner et al.4 criteria for NAFLD fibrosis) would yield different results. Finally, the authors pooled together all patients with chronic liver diseases for the purpose of comparing the diagnostic value of M30 and M65 assays for fibrosis.
We believe that this approach is not methodologically robust and can yield unreliable results. In our own experience, patients with NAFLD and mild fibrosis may display greater levels of M30 compared with those with a diagnosis of Wilson disease and severe fibrosis. It is thus likely that M30 levels are driven chiefly by apoptosis rather than hepatic fibrosis.5, 6 In light of these caveats, a word of caution is needed to avoid overinterpreting the diagnostic utility of M65 assays in the noninvasive assessment of liver fibrosis in chronic liver disease.