What is the false negative rate with the Fecal Immunochemical Test (FIT) for colon cancer screening?

From the Guidelines

The false negative rate for the fecal immunochemical test (FIT) for colorectal cancer screening is approximately 40-42%, as indicated by the most recent and highest quality study 1. This means that about two-fifths of people who actually have colorectal cancer will receive a negative FIT result. The FIT test works by detecting hidden blood in the stool, which can be a sign of colorectal cancer or precancerous polyps. However, not all cancers or polyps bleed consistently, which contributes to the false negative rate. Some key factors associated with false negative results include male sex, family history of CRC, and smoking, as reported in the study 1. The use of aspirin or non-steroidal anti-inflammatory agents could also lead to false positive results, while iron deficiency anaemia and acute diarrhoea may affect the test's accuracy, as noted in the guidelines 1. It's also important to note that FIT is less sensitive for detecting advanced adenomas (precancerous polyps) than for cancer itself, with false negative rates for advanced adenomas being higher. Despite these limitations, FIT remains a valuable screening tool due to its non-invasive nature, low cost, and reasonable sensitivity when performed regularly as recommended. The study 1 highlights the importance of considering these factors when interpreting FIT results and the need for repeated testing to catch cancers that might have been missed in previous screenings. Key points to consider when using FIT for colorectal cancer screening include:

• The test's sensitivity and specificity, as reported in the study 1 and guidelines 1
• The factors associated with false negative results, such as male sex and family history of CRC 1
• The importance of repeated testing to catch cancers that might have been missed in previous screenings 1
• The test's limitations, including its lower sensitivity for detecting advanced adenomas and its potential for false positive results in certain individuals 1.

From the Research

False Negative Rate of Fecal Immunochemical Test (FIT) for Colon Cancer Screening

• The false negative rate of FIT for colon cancer screening is a significant concern, with studies reporting varying rates of false negative results 2, 3, 4.
• A study published in 2015 found that the rate of false-negative results was 66.9% 2.
• Another study published in 2018 found that males, participants with a family history of CRC, hyperglycemia, hypertension, obesity, and (former) smokers were at significantly higher risk for false-negative results 3.
• A study published in 2013 found that the FIT produced a high rate of false-negative results for patients with small or nonpolypoid adenomas, and early-stage cancers were associated with a high rate of false-negative results from the FIT 4.
• The false negative rate of FIT can be influenced by various factors, including demographic characteristics, colonoscopy findings, and potential confounders 2, 3, 4.
• The use of FIT in colon cancer screening can lead to false reassurance after a negative result, and unnecessary colonoscopy after a positive result 2, 3.

Factors Associated with False-Negative FIT Results

• Older age, smoking, and use of aspirin/nonsteroidal anti-inflammatory drugs were associated with lower specificity and higher false-negative rates 2.
• Younger participants, and the use of aspirin/nonsteroidal anti-inflammatory drugs in participants with one FIT with negative results and the absence of high-grade dysplasia were associated with false-negative results 2.
• Males, participants with a family history for CRC, hyperglycemia, hypertension, obesity, and (former) smokers were at significantly higher risk for false-negative results 3.
• Lesion size, location, and morphology can also affect the sensitivity of FIT in detecting colorectal neoplasms 4.

Comparison of FIT with Other Screening Methods

• A study published in 2020 found that mailed multiple-round FITs detect significantly more advanced neoplasia, on a population level, compared with once-only flexible sigmoidoscopy or colonoscopy screening 5.
• Another study published in 2018 found that the yield of CRC in patients with a positive result from the first round of the FIT was 3.7%, and decreased to 1.8% for subsequent rounds 6.