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

Abstract

Context: 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.

Objective: 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.

Design, setting, and participants: 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).

Main outcome measures: 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.

Results: 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).

Conclusion: 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.