NEW YORK (Reuters Health) – Due to hemoglobin degradation, delayed return of fecal occult blood tests (FOBTs) may miss colorectal adenomas and possibly also overt malignancy, according to a report in the International Journal of Cancer for August 15.
FOBTs have become increasingly more accepted in colorectal cancer screening, note the authors, which makes their stability during transport an important variable.
Based on the findings, “Later stage colorectal cancer patients will probably not be missed due to this delay, but at least a relevant proportion of patients with advanced adenomas and possibly stage I colorectal cancer might be missed even with a delay of a few days,” Dr. Leo G. M. van Rossum, from Radboud University Nijmegen Medical Center, the Netherlands, and colleagues state.
The findings stem from a study of 20,623 subjects, 50 to 75 years of age, half of whom who were invited to return an immunochemical FOBT sample for testing. FOBTs (OC-Sensor, Eiken Chemical Co., Tokyo) were returned by 6157 of the subjects who received them (60%), including 3767 (61% of the iFOBT group) who reported the date of sampling.
Overall, 3062 subjects returned the FOBT in under 5 days as recommended. Of the remaining 705 patients, 195 took 7 days or longer to return the test.
With 5 or more days of delay, the odds of detecting an adenoma were reduced by 40%, the researchers report.
In a second part of their study, the researchers retested the FOBT samples of 170 subjects with an initially positive result, defined as a hemoglobin level of 50 ng/mL or higher. Five repeat tests were done in each subject, roughly 2 to 3 days apart. Colonoscopy was performed in 139 of the subjects (82%) and revealed advanced adenomas in 45 cases (32%) and colorectal cancer in 8 (6%).
On average, the authors found that fecal hemoglobin levels fell by 29 ng/mL per day. Among subjects with advanced adenomas, the hemoglobin level was <50 ng/mL in 5 patients (11%) 2 to 3 days after the initial FOBT and in 16 patients (36%) after 10 to 14 days, the authors note.
Two patients (25%) with colorectal cancer had false negative results when FOBT was performed 7 days after the initial test. In both cases, stage I disease was present and the initial hemoglobin level was 100 ng/mL. This level, the authors note, is uncharacteristically low as the average level for stage I disease is 532 ng/mL.
“Until a less sensitive hemoglobin stabilizing buffer is produced, monitoring delay between fecal sampling and laboratory research should be part of quality control for screening with immunochemical FOBT,” the investigators conclude. “Inviting participants to perform a second test when delay is 5 days or more could be considered.”
Int J Cancer 2009;125:746-750.