13C-methacetin breath test as liver function test in patients with chronic hepatitis C virus infection

Background: The C-13-methacetin breath test enables the quantitative evaluation of the cytochrome P450-dependent liver function. Aim: To find out whether this breath test is sensitive in noncirrhotic patients also with chronic hepatitis C in early stages of fibrosis. Methods: Sixty-one healthy controls and 81 patients with chronic hepatitis C underwent a C-13-methacetin breath test. In all patients, a liver biopsy was performed. The liver histology was classified according to the histology activity index-Knodell score. Results: Delta over baseline values of the patients at 15 min significantly differed from controls (19.2+/-9.2parts per thousand vs. 24.1+/-5.7parts per thousand; P<0.003). The cumulative recovery after 30 min in patients was 11.4+/-4.8% and in healthy controls 13.8+/-2.8% (P<0.002). However, patients with early fibrosis (histology activity index IVB) did not differ in delta over baseline values of the patients at 15 min (23.2+/-7.9parts per thousand vs. 22.6+/-7.2parts per thousand; P=0.61) or cumulative recovery (13.6+/-3.7% vs. 13.2+/-3.8%; P=0.45) from patients with more advanced fibrosis (histology activity index IVC). Patients with clinically nonsymptomatic cirrhosis (histology activity index IVD; Child A) metabolized C-13-methacetin to a significantly lesser extent (delta over baseline values of the patients at 15 min: 8.3+/-4.9parts per thousand; P<0.005 and cumulative recovery after 30 min: 5.6+/-3.2%; P<0.003). The C-13-methacetin breath test identified cirrhotic patients with 95.0% sensitivity and 96.7% specificity. Conclusion: The non-invasive C-13-methacetin breath test reliably distinguishes between early cirrhotic (Child A) and noncirrhotic patients, but fails to detect early stages of fibrosis in patients with chronic hepatitis C.