Low-dose aspirin therapy does not appear to compromise the results of immunochemical tests for fecal occult blood, as it may with other types of FOBTs, according to a report in the Dec. 8 issue of JAMA.
The sensitivity of two different immunochemical FOBTs for detecting colorectal neoplasms was actually higher among patients taking low-dose aspirin therapy than among those not taking aspirin, particularly in cases of advanced neoplasms, said Dr. Hermann Brenner and his associates in the division of clinical epidemiology and aging research, German Cancer Research Center, Heidelberg.
Concerns have been raised that low-dose aspirin therapy might cause bleeding from upper GI lesions or insignificant colonic lesions, which would produce false-positive FOBT results. Some physicians have even called for suspension of aspirin therapy before FOBT.
But immunochemical FOBTs (iFOBTs) react to globin, which is degraded as it passes through the gastrointestinal tract. They are less likely to produce false-positives from upper GI bleeds than are the guaiac-based FOBTs that react to the heme moiety of hemoglobin, which is more stable as it passes through the digestive system.
Dr. Brenner and his colleagues assessed the relationship between aspirin therapy and iFOBT results in a large sample of adults participating in a screening colonoscopy program at 20 GI practices across southern Germany. The 1,979 study subjects (mean age, 62 years) provided stool samples before undergoing bowel preparation for colonoscopy.
A total of 233 of these subjects (12%) were taking low-dose aspirin therapy for cardiovascular prophylaxis, while the remainder had never used low-dose aspirin. The prevalence of neoplasms found on colonoscopy was similar between the two groups.
The study also found that two different iFOBTs had substantially (about 30%) higher sensitivity in detecting any neoplasm in people using aspirin therapy than in nonusers. The difference in test sensitivity was greatest in people found to have advanced malignancies, with one of the iFOBTs achieving a sensitivity of 71% among those using aspirin therapy but only a sensitivity of 36% among nonusers (P = .001).
This enhanced sensitivity was consistent across various subgroups of patients and across a broad range of cut points for test positivity. The advantages of aspirin therapy were particularly marked in men: among men taking low-dose aspirin, the sensitivity of iFOBTs was up to 46 percentage points higher than it was in men not using aspirin therapy, the investigators said (JAMA 2010;304:2513-20).
In contrast, the specificity of iFOBTs was slightly (about 5%) lower in people using aspirin therapy than in nonusers.
These findings indicate that "there is no need to stop low-dose aspirin use prior to undergoing iFOBT," Dr. Brenner and his associates said.
"On the contrary, our results may even raise the provocative suggestion of whether temporary use of low-dose aspirin might be considered to enhance performance of iFOBTs," they said.
Given their findings, temporary use of low-dose aspirin might yield a sensitivity for detecting advanced neoplasms of 60%-70% at a specificity of approximately 90% – levels of sensitivity and specificity that exceed those of other established stool tests and that "might come close to the sensitivity of sigmoidoscopy," the researchers noted.
However, it would be premature to make such a recommendation before these findings are replicated in other populations "and followed up in further research, ideally including randomized trials and different types of FOBTs," they added.
This study was somewhat limited in that despite the large sample size, there were few advanced neoplasms, resulting in broad confidence intervals around some estimates of iFOBT performance, Dr. Brenner and his colleagues said.
The study was supported in part by the German Research Foundation and the German Federal Ministry of Education and Research. The test kits were provided free of charge by the manufacturer. Dr. Brenner reported that the German Cancer Research Center has received funding from Eiken Chemical to evaluate an iFOBT that was not included in this analysis. Also, a patent application was filed at the European Patent Office for the combination of low-dose aspirin use and iFOBTs in early detection of colorectal neoplasms.