Negative CLOtest pellet can be reused

The CLOtest is based on the production of ammonia from urea in the presence of urease. In theory, substrate that has not been consumed in a negative test can be reused.

We collected negative CLOtest pellets after their first use and stored them at room temperature. Whenever a CLOtest was needed during endoscopy, two biopsy specimens were taken from the antrum. One specimen was tested with a new CLOtest and the other with one that had been used previously. Time to color change was observed in paired tests.

We used 216 previously used CLOtest pellets with biopsy specimens obtained from 317 patients. Of the paired tests, 204 matched positive and 108 tested negative. Only 5 paired tests had discrepant results. Three had positive results only with a new CLOtest, and 2 were positive only with the reused test. In positive paired tests, there was significant linear correlation in log-transformed color change time between reused and new tests (p < 0.001). Ninety-two percent of previously used pellets were reused fewer than three times before they yielded a positive color change; the interval to this occurrence ranged from 2 to 15 days. Compared with the new CLOtest, the sensitivity of the reused CLOtest was 98. 6% and the specificity was 98.2%.

A negative CLOtest kept at room temperature can be reused within a short period of time, in circumstances in which there are environmental and economic considerations to be taken into account.