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Delaying colonoscopy after abnormal stool test increases risk of CRC

Tue, 02/02/2021 - 12:11
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A Veterans Affairs study has reported  that delays in undergoing colonoscopy following an abnormal stool test increase the risk of a colorectal cancer (CRC) diagnosis and cancer-related death. In a retrospective study of more than 200,000 Veterans, the researchers found that patients who received colonoscopy more than 13 months after an abnormal stool blood test were up to 1.3 times more likely to have CRC, compared with those who had colonoscopy up to three months after the stool test. Odds of an advanced stage of cancer at diagnosis were up to 1.7 times higher when colonoscopy was delayed beyond 16 months.

The findings reported in the paper, ‘Time to Colonoscopy After Abnormal Stool-Based Screening and Risk for Colorectal Cancer Incidence and Mortality’, published in the journal Gastroenterology, also showed the risk of CRC-related death increased by up to 1.5 times when colonoscopy was delayed more than 19 months. This was the first study in the US, the researchers noted, to examine the risk of death linked to delays in undergoing a colonoscopy following an abnormal stool blood test.

For the study, the researchers examined the association between time to colonoscopy and CRC outcomes among individuals who underwent diagnostic colonoscopy after abnormal stool-based screening. They performed a retrospective cohort study of 204,733 veterans age 50-75 years with an abnormal faecal occult blood test (FOBT) or faecal immunochemical test (FIT) between 1999 and 2010. Using multivariable Cox proportional hazards, they generate CRC-specific incidence and mortality hazard ratios (HRs) and 95% confidence intervals (CI) for three-month colonoscopy intervals, with one to three months as the reference group. Association of time to colonoscopy with late-stage CRC diagnosis was also examined.

Many health care experts believe that stool tests, such as FIT, are as reliable as colonoscopy in screening for colorectal cancer. The use of stool tests has increased during the COVID-19 pandemic because of the convenience and safety of home testing and because patients may be reluctant to go to a health care facility for colonoscopy.

Dr Samir Gupta, chief of gastroenterology at the VA San Diego Healthcare System, co-authored the study. Many patients and some primary care providers do not understand the importance of having colonoscopy after an abnormal stool test, he explained.

"Some patients and providers even explain these results incorrectly, attributing abnormal results to haemorrhoids, something that was eaten or other problems," he added. "They don't believe the results. The results of this study should raise awareness that delaying colonoscopy after an abnormal stool test can have major consequences, including increased risk for cancer diagnosis, late-stage cancer at diagnosis, and death from colorectal cancer. These findings can also help motivate patients and providers to make sure colonoscopies are completed after an abnormal test."

The study findings will have even greater implications as more non-invasive tests for CRC screening come on the market, said Gupta.

"With stool tests, such as FIT and FIT-DNA, already covered by most insurance companies and with promising new blood-based screening tests for CRC under study in large trials," he said. "The challenge of ensuring complete screening, including initial completion and follow through to colonoscopy after an abnormal test, is likely to grow substantially."

"These findings extend current knowledge about the clinical implications of time to follow-up after abnormal FIT-FOBT. Further work should include [efforts] that address barriers to [undergoing] colonoscopy after abnormal non-colonoscopic screening results and policies to encourage the routine monitoring of follow-up rates,” the researchers concluded. "Currently, there is no national policy or standard for the clinically acceptable time interval between an abnormal FIT-FOBT result and diagnostic colonoscopy. Time to colonoscopic follow-up varies widely in practice and across health care settings. A recommended interval that is too long can contribute to polyp progression and stage migration of CRC, risking the need for more aggressive and morbid treatment, as well as less favourable outcomes."