NEW YORK (Reuters Health) – While qualitative immunochemical fecal occult blood tests (FOBTs) may offer advantages over traditional guaiac-based FOBTs for colorectal cancer screening, there are large differences in performance characteristics between the various immunochemical FOBTs, new research indicates.

False-positive results are a problem with guaiac-based FOBTs, according to the report in the Annals of Internal Medicine for February 3. The immunochemical FOBTs attempt to remedy this problem and improve sensitivity by using antibodies against specific blood components. Whether they have been successful in this effort, however, is unclear as few large-scale, colonoscopy-based studies have examined this topic.

In the current study, Dr. Ulrike Haug, from the German Cancer Research Center, Heidelberg, and colleagues evaluated the ability of six qualitative immunochemical FOBTs to identify colorectal adenomas in 1319 subjects who were undergoing screening colonoscopy. The subjects were 63 years of age, on average, half were female, and all were considered to be at average risk for colorectal neoplasia.

All six tests were applied to stool samples obtained prior to the bowel preparation for colonoscopy, the investigators note.

An adenoma was found on colonoscopy in 405 subjects (31%), including 130 (10%) with an advanced adenoma.

As noted, performance varied widely between the immunochemical FOBTs. In detecting advanced adenomas, sensitivity ranged from 25% to 72%, while specificity ranged from 70% to 97%. A guaiac-based FOBT was 9% sensitive and 96% specific.

Two tests — the immoCARE-C and FOB advanced — showed the best overall performance with sensitivities of 25% and 27%, respectively, and specificities of 97% and 93%, respectively. The corresponding positive likelihood ratios were 3.5 and 2.5.

“Our results demonstrate the qualitative immunochemical FOBTs could be an option for future colorectal cancer screening, combining the advantages of immunochemical FOBT (improved detection of precancerous lesions) with the same or greater simplicity and practicality for mass screening as offered by the widely used guaiac-based FOBT,” the team concludes.

However, they add, “Careful evaluation of each test variant is needed given the large differences in diagnostic performance among tests.”

Reference:
Ann Intern Med 2009;150:162-169.