Objectives: Xylose absorption testing has traditionally involved measurement of serum xylose and/or measurement of excreted xylose in urine. However, by enriching xylose with a 13C- or 14C-isotope, absorption of an oral xylose load will be reflected in the time-dependent pattern of 13CO2 or 14CO2 exhaled in breath. Our objectives were to evaluate the diagnostic properties of 13C-xylose and 14C-xylose breath tests in coeliac disease, and to develop a diagnostic breath test index.
Material and methods: We reviewed data from 41 coeliac patients who underwent the 14C-xylose breath test before and after commencement of a gluten-free diet, and 60 coeliac patients who underwent the 13C-xylose breath test, 37 of whom repeated the test after starting a gluten-free diet. Coeliac patients were compared with healthy control subjects.
Results: Coeliac patients exhaled significantly less 13CO2 or 14CO2 than healthy controls during the first hour of the test and more isotope-labelled CO2 than control subjects after 3 h. Diagnostic accuracy was optimal with test duration of 210 min combining gas measurements at 30 min and 210 min in a simple fraction. This gas fraction index (30 min/210 min) distinguished between coeliac patients and healthy control subjects with 84-95% sensitivity and 87-94% specificity. After commencement of a gluten-free diet, the gas fraction index increased in most coeliac patients, but remained lower than that in healthy control subjects.
Conclusions: 13C-xylose- and 14C-xylose breath tests discriminate between coeliac patients and healthy control subjects with high sensitivity and specificity. The stable isotope 13C-xylose breath test has comparable diagnostic accuracy to the radioactive isotope 14C-xylose breath test and should be the preferred alternative to traditional xylose absorption tests.