Digital rectal examination sampling of stool is less predictive of significant colorectal pathology than stool passed spontaneously.
ABSTRACT To compare the positivity rate and the positive predictive value of an immunochemical faecal occult blood test (FOBT) carried out by using stool samples obtained during a routine screening method and those obtained during digital rectal examination.
Screening programme-based, cross-sectional study.
In a screening programme-based, cross-sectional study, 1,044 subjects who received both an immunochemical FOBT and colonoscopy were divided into two groups according to stool collection techniques--the routine screening method and the digital rectal examination method. The positivity rate of the immunochemical FOBT, as well as the positive predictive value for colorectal cancer and large adenomatous polyp, were determined in the two groups.
The positivity rate and positive predictive value were 3.8% and 60.0% (10.0% for cancer and 50.0% for adenomatous polyp) in the routine screening group, and 9.4% and 26.5% (4.1% for cancer and 22.4% for adenomatous polyp) in the digital rectal examination group, respectively, indicating a significant difference in the positivity rate (P < 0.01) as well as the positive predictive value (P< 0.05) between the two groups.
These results show that digital rectal examination sampling of stool is less predictive of significant colorectal pathology than stool passed spontaneously, and therefore the latter is the preferred method for stool sampling.