Low-dose aspirin use and performance of immunochemical fecal occult blood tests

Immunochemical fecal occult blood tests (iFOBTs) are potentially promising tools for colorectal cancer screening. Low-dose aspirin use, which increases the likelihood of gastrointestinal bleeding, is common in the target population for colorectal cancer screening.

To assess the association of low-dose aspirin use with the performance of 2 quantitative iFOBTs in a large sample of patients undergoing colorectal cancer screening.

Diagnostic study conducted from 2005 through 2009 at internal medicine and gastroenterology practices in southern Germany including 1979 patients (mean age, 62.1 years): 233 regular users of low-dose aspirin (167 men, 67 women) and 1746 who never used low-dose aspirin (809 men, 937 women).

Sensitivity, specificity, positive and negative predictive values, and area under receiver operating characteristic (ROC) curves in detecting advanced colorectal neoplasms (colorectal cancer or advanced adenoma) with 2 quantitative iFOBTs.

Advanced neoplasms were found in 24 users (10.3%) and 181 nonusers (10.4%) of low-dose aspirin. At the cut point recommended by the manufacturer, sensitivities of the 2 tests were 70.8% (95% confidence interval [CI], 48.9%-87.4%) for users compared with 35.9% (95% CI, 28.9%-43.4%) for nonusers and 58.3% (95% CI, 36.6%-77.9%) for users compared with 32.0% (95% CI, 25.3%-39.4%) for nonusers (P = .001 and P = .01, respectively). Specificities were 85.7% (95% CI, 80.2%-90.1%) for users compared with 89.2% (95% CI, 87.6%-90.7%) for nonusers and 85.7% (95% CI, 80.2%-90.1%) for users compared with 91.1% (95% CI, 89.5%-92.4%) for nonusers (P = .13 and P = .01, respectively). The areas under the ROC curve were 0.79 (95% CI, 0.68-0.90) for users compared with 0.67 (95% CI, 0.62-0.71) for nonusers and 0.73 (95% CI, 0.62-0.85) for users compared with 0.65 (95% CI, 0.61-0.69) for nonusers (P = .05 and P = .17, respectively). Among men, who composed the majority of low-dose aspirin users, the areas under the ROC curve were 0.87 (95% CI, 0.76-0.98) for users compared with 0.68 (95% CI, 0.63-0.74) for nonusers and 0.81 (95% CI, 0.68-0.93) for users compared with 0.67 (95% CI, 0.61-0.72) for nonusers (P = .003 and P = .04, respectively).

For 2 iFOBTs, use of low-dose aspirin compared with no aspirin was associated with a markedly higher sensitivity for detecting advanced colorectal neoplasms, with only a slightly lower specificity.