Aspirin, currently on the list of drugs to avoid before undergoing screening for fecal occult blood, might not interfere with immunochemical forms of the test, according to a JAMA study.

As part of their preparation for screening colonoscopy, some 2000 patients were asked about regular use of drugs, including low-dose aspirin. All patients underwent two different immunochemical fecal occult blood tests (iFOBTs) to measure hemoglobin and hemoglobin-haptoglobin.

Based on the colonoscopy findings, iFOBT sensitivity results for advanced neoplasms were as follows:

Specificities were slightly lower for aspirin users than nonusers (e.g., 85.7% vs. 91.1% for the hemoglobin-haptoglobin test).

The authors conclude: “Our study strongly suggests that use of low-dose aspirin does not hamper testing for fecal occult blood by immunochemical tests. On the contrary, our findings raise the hypothesis that test performance may be enhanced by temporary use of low-dose aspirin, a hypothesis that needs replication in larger samples and followed up in further research.”