Colorectal adenomatous polyps detected by immunochemical occult blood screening

This study aimed to evaluate the validity of immuno-chemical occult blood screening for colorectal adenomas and to clarify the characteristics of this disease which are detected.

We studied 140 colorectal adenomas and 140 healthy controls in a hospital based case control study, in which three-day testing was conducted to assess the accuracy of the immuno-chemical occult blood screening test (total 280 patients). A further 80 colorectal adenomas 1 cm or larger, which were detected by a screening program, were compared with matched cases detected by the outpatient clinics (total 160 patients). A comparison of characteristics including tumor location, shape and histology was made between the two groups.

Sensitivity and specificity were calculated to be 46% (61% for tumors larger than 1 cm, 30% for those less than 1 cm), and 96% respectively, showing a significant difference in sensitivity between large and small adenomas (p < 0.01). The proportion of rectal adenomas was significantly higher in the outpatient clinics (41%) than in the screening program (21%) (p < 0.05), whereas no differences were noted in the other measures.

These results suggest that immuno-chemical occult blood is inadequate as a screening test for detecting small adenomas, as t can not differentiate between the detection of rectal adenomas from large adenomatous polyps.