Lower specificity of occult-blood test on stool collected by digital rectal examination.

BACKGROUND/AIMS: To compare the diagnostic accuracy of an immunochemical fecal occult-blood test for colorectal cancer between the stool specimens obtained during the routine screening and those during the digital rectal examination.

METHODOLOGY: One hundred and fourteen patients with colorectal cancer and 228 healthy controls served as subjects of the study. Fecal occult-blood was tested by both of two methods; by the routine screening and by the digital rectal examination, and the sensitivity and specificity of an immunochemical fecal occult-blood test were determined in these two methods.

RESULTS

The sensitivity and specificity were 79.8% and 96.5% in the routine screening method, and 86.0% and 79.8% in the digital rectal examination method, respectively, showing a significant difference in the specificity (P < 0.01) between these two stool collection methods. There was no significant difference in the sensitivity between these two stool collection methods.

CONCLUSIONS

These findings indicate that the stool specimens collected at the time of the digital rectal examination is not suitable for testing of fecal occult-blood.