13C-xylose and 14C-xylose breath tests for the diagnosis of coeliac disease.

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.