Faulty Samples Frustrate FIT Screening for Colorectal Cancer 

Stool test for signs of cancer, often collected at home, sometimes fails due to inadequate sampling, according to a study in the AACR Journal Cancer Epidemiology, Biomarkers & Prevention.

About a tenth of the fecal immunochemical (FIT) tests used for routine colorectal cancer (CRC) screening in a Texas health system contained unsatisfactory samples and couldn’t be processed, according to a study published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research (AACR). 

Rasmi Nair, MBBS, PhD
Rasmi Nair, MBBS, PhD

“With the advent of other home tests, such as stool DNA tests for CRC screening and human papillomavirus tests for cervical cancer screening, understanding the reasons for unsatisfactory home tests, implementing administrative systems to track those tests, and automatic subsequent testing and follow-up are becoming even more important,” said Rasmi Nair, MBBS, PhD, co-first author of the paper and an assistant professor at the Peter O’Donnell Jr. School of Public Health of UT Southwestern Medical Center. 

FIT is a self-collected test that looks for hidden blood in the stool as a potential marker for CRC. FIT is recommended by the US Preventive Services Task Force for annual CRC screening among people from the age of 45 to 75. For many—including uninsured and lower-income individuals, as well as those from medically underrepresented groups—FIT may be cheaper and more accessible than a colonoscopy or other stool-based tests that look for DNA that may indicate the presence of a tumor.  

“FIT is the test of choice, particularly in large population-based settings where access to screening colonoscopy is limited,” Nair said. “Even when colonoscopy is available, many would prefer to do the simple, noninvasive stool test.” 

However, researchers have been unsure how often the screening fails because of problems with sample collection, labeling, or storage, said Po-Hong Liu, MD, a gastroenterology fellow at UT Southwestern Medical Center and co-first author of the study. It is also unclear how often patients who submit unsatisfactory samples are given the opportunity to try the test again. 

Po-Hong Liu, MD
Po-Hong Liu, MD

“The effectiveness of FIT depends on the satisfactory completion of multiple steps—participation, test completion, follow-up of abnormal results, and repeat testing annually,” Liu explained. “A break in the chain at any point can reduce the effectiveness of CRC screening.” 

Nair, Liu, and colleagues examined the history of 56,980 individuals aged 50 to 74 who underwent FIT screening between 2010 and 2019 within the Dallas-based Parkland Health system, a safety-net health system that primarily provides care to uninsured, lower-income, and racial/ethnic minority individuals. The tests were performed at health care offices or via a mail order system, the latter of which automatically sent a repeat test to individuals with an initial unsatisfactory result. 

Overall, 10% of tests were found to be unsatisfactory. The testing laboratories recorded the reasons as:  

  • inadequate specimen (51%) 
  • incomplete labeling (27%) 
  • sample too old (13%) 
  • broken or leaking container (8%).  

Furthermore, only 41% of individuals with unsatisfactory tests received follow-up FIT or colonoscopy screening within 15 months of the failed test. 

“The fact that, in most instances, unsatisfactory FIT was not followed by a timely subsequent test highlights the need for systems to have a better, more comprehensive approach to tagging and following up unsatisfactory FIT,” Liu said. 

Mail-order tests were almost three times more likely to produce unsatisfactory results than tests performed in a clinic, which the authors speculated may reflect the technical assistance available in a clinic setting. However, likely due to the automatic distribution of a repeat test, patients with unsatisfactory mail-order tests were twice as likely to undergo repeat screening within 15 months. 

The study also found racial and ethnic disparities in satisfactory FIT completion: Black patients were nearly one and a half times more likely to submit an unsatisfactory test than non-Hispanic whites, and patients who primarily speak Spanish were 1.12 times more likely to submit an unsatisfactory test. 

Based on these data and those from previous studies, the authors suggested several potential solutions to improve complete and accurate sampling. These included wordless or low-literacy instruction pamphlets to eliminate language and literacy barriers; pre-affixed patient labels or barcodes to minimize labeling errors; and automated systems for identifying and contacting patients with unsatisfactory tests.