C-13-UREA BREATH TEST FOR HELICOBACTER-PYLORI - CUTOFF POINT DETERMINATION BY CLUSTER-ANALYSIS

1. This study was performed on a large set of C-13-urea breath test re sults to determine the optimal cut-off point of the test for the diagn osis of Helicobacter pylori (Hp) infection. 2. The following steps wer e applied to three sets of urea breath test results obtained in three groups of subjects (696 adults before anti-Hp treatment, 1056 adults a fter anti-ap treatment and 173 children under 17 years of age): (1) de monstrate the distribution of urea breath test results as a mix of two normal populations (Hp negative and Hp positive) by logarithmic trans formation of the results in each group of subjects; (2) apply statisti cal cluster analysis to determine the separation point between Hp-nega tive and -positive populations; (3) calculate the mean and SD of each population, and use these parameters in the equation of the normal dis tribution to establish the frequency curves of Hp-negative and -positi ve populations; and (4) determine the cut-off point of the urea breath test as the intersection of the two curves, and the risks of error re lated to it. 3. The optimal cut-off point was found at +3.00 delta par ts per thousand, with a risk of false-negative or -positive response o f the urea breath test of less than 3%, From this, a cut-off point of +3.00 delta parts per thousand for the C-13-urea breath test is recomm ended, with an indetermined zone between +2.5 and +3.5 delta parts per thousand to account for the spontaneous variation of (CO2)-C-13 in br eath and the limits of GC-isotope ratio-MS analytical precision.