Short-term low-dose aspirin use prior to immunochemical fecal occult blood testing (iFOBT) significantly increased the test’s sensitivity for detecting advanced colorectal tumors, new study findings indicate.

Previously, health officials voiced concerns that an adverse event associated with aspirin use ­— an increased risk of upper gastrointestinal bleeding — could compromise the specificity of the test. If iFOBTs pick up on bleeding from sources other then colorectal neoplasm, officials believed that it could increase the likelihood of false-positive test results.

This is concerning because low-dose aspirin use to prevent primary and secondary cardiovascular disease is common among age groups most often screened for colorectal cancer, and some health care providers have suggested halting aspirin use prior to iFOBT screening.

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Hermann Brenner, MD, MPH, of the German Cancer Research Center in Heidelberg, Germany, and colleagues, measured the sensitivity and specificity of two quantitative iFOBT (a hemoglobin and a hemoglobin-haptoglobin test) in 1,979 patients (mean age, 62.1 years) at internal medicine and gastroenterology practices in Southern Germany. Results were published in the Dec. 8 Journal of the American Medical Association.

“For both tests, sensitivity was markedly higher, while specificity was slightly lower among users of low dose aspirin compared with nonusers,” the researchers wrote.

They detected advanced neoplasms in 24 regular low-dose aspirin users (n=233; 10.3%) and in 181 nonusers (n=1,746; 10.4%).  Sensitivity and specificities for the tests were as follows:

  • Hemoglobin test – sensitivity for low-dose aspirin users was 70.8% vs. 35.9% in nonaspirin users; specificity for users was 85.7% vs. 89.2% for nonusers.
  • Hemoglobin-haptoglobin test – sensitivity for low-dose aspirin users was 58.3% vs. 32% for nonusers; specificity for users was 85.7% vs. 91.1% for nonusers.

“These patterns were consistent across a broad range of relevant cut points for test positivity,” the researchers wrote. “Receiver operating characteristic analyses revealed sensitivity to be mostly much higher at comparable levels of specificity, with substantially larger areas under the curve among users of low-dose aspirin.”

The findings still need to be replicated, according to the researchers, who called for further research in larger randomized samples with different types of FOBTs.