13C-breath tests and liver fibrosis.
The evaluation of the presence and degree of liver fibrosis in patients with chronic liver disease is a fundamental diagnostic and prognostic issue. This is mainly due to the repercussions of liver fibrosis on liver function, whose derangement, in turn, is mainly responsible for the negative events of advanced liver disease. 13C-Breath Tests ((13/14)C-BTs) for the study of liver function were developed more than twenty years ago in order to non-invasively assess residual liver function in patients with various degrees of liver fibrosis, from minimal stages up to liver cirrhosis. Sequential studies that were performed over the years using various 13C-BT substrates showed that increasing degrees of liver fibrosis are paralleled by concomitant modifications in 13C-BT results. The 13C-BT probes that reportedly obtained interesting results were aminopyrine, galactose, and more recently phenylalanine. As the knowledge in this field evolved, probes for the study of specific functions, such as the 13C-Octanoate Breath Test were sought. Analysis of the published studies would seem to show that 13C-BTs alone, or in combination may provide a non-invasive picture of the functional alterations secondary to liver fibrosis. Further studies are needed to evaluate the diagnostic yield of the 13C-BT in particular clinical situations, such as in patients with normal static parameters of liver function, or after therapy.