Screening for colorectal cancer by use of guaiac-based fecal occult blood tests reduces disease-specific mortality.
However, due to imperfect specificity, about half of individuals positive for guaiac fecal occult blood tests are negative for neoplasia on colonoscopy.
Dr Callum Fraser and colleagues from Scotland assessed whether a screening program for colorectal cancer could assist with colonoscopy selection.
The team evaluated whether testing those positive for guaiac fecal occult blood tests, could select more appropriately those who should receive colonoscopy.
Immunochemical fecal occult blood tests were used in the assessments.
The team included 1486 individuals who were guaiac fecal occult blood test positive in the second screening.
|The sensitivity of a positive result for cancer was 95%|
The patients gave 2 samples, each from separate stools, for immunochemical fecal occult blood tests while awaiting colonoscopy.
The team compared immunochemical findings with those from colonoscopy using odds ratios of positive versus negative samples.
Sensitivity, specificity, and positive and negative likelihood ratios for cancer, and for cancer and high-risk adenomatous polyps were also calculated.
The researchers reported that 54% of sets of duplicate samples were returned for analysis.
The team found no evidence of sampling bias with regard to sex, age, or
degree of positivity on guaiac fecal occult blood tests.
The researchers noted that 22% of samples were negative, 16% were negative and positive, and 62% were positive.
The test showed a highly significant positive correlation between degree of
positivity on guaiac and on immunochemical fecal occult blood tests.
The team reported that 795 individuals had data for colonoscopy.
Both negative and positive participants had colorectal cancer.
The research team found adenomatous polyps in 16% of negative individuals, 19% of negative and positive individuals, and 39% of positive individuals.
Normal colonoscopy was less common in the positive group than in the negative only, or in the combined negative and positive groups.
The odds ratio for positive results associated with cancer was about 8, and with high-risk adenomatous polyps was about 3.
The team observed that sensitivity of a positive result for cancer was 95%.
The sensitivity of a positive result for high-risk adenomatous polyps was 90%.
Specificity was 40% and 48%, respectively.
Dr Fraser's team concluded, “Immunochemical fecal occult blood tests for individuals with positive guaiac fecal occult blood tests could decrease substantially the number of false positives in a screening program for colorectal cancer."