Cut-off point, timing and pitfalls of the C-13-urea breath test as measured by infrared spectrometry

Background. The best timing and the best cut-off level of the C-13-urea bre ath test have not yet been well established. Aims. To evaluate the cut-off value and the influence of medication on the C-13-urea breath test as measured by infrared spectrometry. Methods. A series of 223 patients, sent for endoscopy, performed C-13-urea breath test in fasting conditions with 75 mg of C-13-urea and 20 mi of citr ic acid. Breath samples were collected before and then 10, 20, 25 and 30 mi nutes after ingestion. As gold standard, histological examination of gastri c biopsies was used. A questionnaire was completed concerning the intake of medication, likely to influence the test, in the 2 months preceding the te st. Sensitivity, specificity, positive predictive value and negative predic tive value at 10 20, 25 and 30 minutes at different cut-off values (3, 3.5, 4, 4.5, 5.00/00 DOB) were calculated. Results. A total of 182 patients did not take medication. There was no sign ificant difference between the different cut-off levels at different times. Compared with the group of 41 patients who did take medication, likely to influence the test, the differences were significant (Fisher exact test) Conclusion. There was no significant difference between the different cut-o ff values. A 10-minute test with a cut-off level between 4 and 5% delta ove r baseline (sensitivity: 100%, specificity: 95%) is, therefore, proposed. T o avoid false negative results due to unknown intake of medication, every p atient submitted to the C-13-urea breath test should fill out a questionnai re.