Immunological faecal occult blood testing: a discriminatory test to identify colorectal cancer in symptomatic patients

Introduction: Current investigation for patients with colorectal symptoms without overt rectal bleeding is undertaken by colonoscopy or by flexible sigmoidoscopy and barium enema. A large majority of patients do not have colorectal cancer. There exists no instant, objective measure to discriminate patients who are likely to have colorectal cancer and therefore require expedient investigation.

Aim: To evaluate the sensitivity and specificity of immunological faecal occult blood testing (FOBT) in patients with colorectal symptoms without overt rectal bleeding.

Methods: Consecutive patients referred for urgent colonic investigation, were prospectively studied. A faecal sample was obtained from each one and subjected to immunological FOB which tested either negative or positive. All patients then underwent complete colonic imaging. The correlation between FOBT status and results from colonic imaging was studied.

Results: Of 126 tested, thirty patients (26.8%) were FOBT positive. One hundred and twelve patients underwent complete colonic imaging. In the FOBT positive group colonic imaging identified 17 cases of histologically proven adenocarcinoma, 1 recurrent squamous cell carcinoma of anus, 1 adenomatous polyp, 6 cases of diverticulosis, and no pathology in 5 cases. In the 82 FOBT negative patients, no cancers were found. Overall the Immunological Faecal Occult Blood Test was found to have 100% sensitivity and 86.3% specificity.

Conclusion: Immunological faecal occult blood testing is a sensitive and specific test in identifying colorectal cancer and may be useful in identifying those patients who warrant urgent investigation. Routine clinical application may be useful in the allocation of resources.