Stool Tests: A Powerful Tool for Early Colon Cancer Detection

Improving Diagnostic Pathways for Colorectal Cancer with Fecal Immunochemical Tests

The Challenge of Bowel Symptoms in Diagnosing Colorectal Cancer

Bowel symptoms are often unreliable indicators of colorectal cancer (CRC), as they can arise from various other conditions. Due to the serious nature of bowel cancer, patients exhibiting symptoms are typically referred for tests to exclude the possibility of cancer. Alarmingly, 96 out of 100 patients who receive an urgent referral do not have CRC, highlighting inefficiencies in the diagnostic process.

Recommendations by NICE on Fecal Immunochemical Tests

Since 2017, the National Institute of Health and Care Excellence (NICE) has advocated for the use of fecal immunochemical tests (FIT) as a screening tool. However, FIT is not currently recommended for all symptomatic patients; its use is restricted to those with low-risk symptoms, primarily due to concerns regarding its diagnostic accuracy.

Study Overview: Accuracy of FIT in Detecting Colorectal Cancer

A recent study published in the journal *Gut* evaluates the effectiveness of FIT as a predictive tool for colorectal cancer. FIT operates by identifying blood in the stool, specifically targeting the globin portion of the hemoglobin molecule found in red blood cells. Conducted across 50 NHS hospitals in England, the study involved patients referred for investigative colonoscopy, who were also asked to provide a fecal sample.

To ensure unbiased results, a double-blinded approach was utilized, meaning colonoscopists were unaware of any FIT lab results, and lab processing occurred without knowledge of the patient’s colonoscopy status. The primary objective was to assess how effectively FIT results aligned with the “gold standard” of colonoscopy in detecting CRC.

Analysis and Key Findings

The analysis included 9,822 patients who provided valid FIT and colonoscopy results. The key measures of diagnostic accuracy were sensitivity and specificity. Sensitivity refers to a test’s ability to accurately identify individuals with a specific condition (CRC), while specificity measures the ability to correctly identify those without the condition.

This study evaluated FIT performance at three thresholds: 2ug, 10ug, and 150ug of hemoglobin per gram of feces. At the 2ug threshold, FIT demonstrated a sensitivity of 97%, correctly identifying 319 of the 329 individuals diagnosed with CRC via colonoscopy. However, increasing the threshold to 10ug reduced sensitivity to 90.1%, and further increasing it to 150ug resulted in a sensitivity drop to 70.8%. At this level, FIT accurately identified only 233 of the 329 CRC patients, as 96 patients had hemoglobin levels below the 150ug/g threshold.

Evaluating Specificity in Screening Tools

Specificity is crucial for a screening tool, as it indicates the test’s ability to correctly identify patients without CRC. At the lowest threshold of 2ug, FIT returned negative results for 6,157 out of 9,493 patients without CRC, while 3,336 were incorrectly flagged as positive, resulting in a specificity of 64.9%. As the positivity threshold increased, so did specificity; at 10ug, specificity rose to 83.5%, and at 150ug, it reached 94.6%.

Determining the optimal threshold depends on several factors, including the estimated prevalence of CRC in the population and the capacity of the health service to perform colonoscopies. Using the 2ug threshold would result in 97% of CRC patients being referred for colonoscopy, but it would also lead to approximately one-third of patients without CRC undergoing unnecessary procedures.

Currently, NICE suggests using the 10ug threshold, which this study indicates has a sensitivity of 90.1% and a specificity of 83.5%. However, if the health service can accommodate it, the advantages of the lower 2ug threshold are notable. Not only does it lead to more CRC patients being referred for colonoscopies, but it also provides a higher negative predictive value (NPV). At the 2ug threshold, the NPV for CRC was 99.8%, indicating a high likelihood that a negative FIT result signifies the absence of CRC.

Conclusion and Recommendations

The findings of this study strongly endorse the integration of FIT into the diagnostic pathway for colorectal cancer. The results suggest that NICE may need to reevaluate its current recommendations regarding the optimal threshold and consider expanding the patient population eligible for FIT screening.