The influence of warming on rapid urease test results: a prospective evaluation

A rapid urease test is the initial test of choice for the diagnosis of Helicobacter pylori at endoscopy. Incubating the CLOtest at 30 degrees to 40 degrees C is recommended, but this decreases simplicity and requires the purchase of additional equipment. We compared results of testing at room temperature versus incubation at 37 degrees C.

Four biopsy specimens were taken from the same portion of the antrum in 200 patients undergoing upper endoscopy. One was placed in each of two CLOtests and two were sent for histologic examination. One CLOtest was incubated at 37 degrees C while the other remained at room temperature (22 degrees to 24 degrees C). Tests were checked every 15 minutes for the first 3 hours, every 1 hour from 3 to 6 hours, and at 24 hours.

One hundred twenty one (61%) of 200 patients had H. pylori on histologic examination. Median time to a positive test was 3/4 hour at 37 degrees C and 1 hour at room temperature (p < 0.0001). Sensitivities were greater at 37 degrees C at 1 hour (70% vs 49%; p = 0.001) and 2 hours (86% vs 76%, p = 0.07), but were nearly identical thereafter. Specificities, identical at the two temperatures, were 99% to 100% at 1 to 6 hours and 95% at 24 hours. The CLOtest became positive more rapidly at 37 degrees C in 72% of patients: more than 1/2 hour faster in 42%; and more than 1 hour faster in 16% of patients.

Incubation of the CLOtest at 37 degrees C hastens the time to a positive test in most patients, although the time saved is usually less than 1 hour. Sensitivity is improved when the test is read at 1 to 2 hours, but no improvement is seen beyond this time. Specificity is not influenced by warming. CLOtest incubation at 37 degrees C should be done if a final reading of the CLOtest is desired within 1 to 2 hours of biopsy.