The Fecal Immunochemical Test (FIT) is a simple, non-invasive screening tool used primarily to detect signs of colorectal cancer. This at-home test identifies minute traces of human hemoglobin, a protein found in red blood cells, in the stool. The presence of hidden blood, invisible to the naked eye, can indicate bleeding from polyps or cancers in the lower gastrointestinal tract. Because the test specifically looks for human hemoglobin, it is not affected by dietary restrictions or most medications. Understanding the correct collection technique is crucial for obtaining an accurate result and avoiding the need for a repeat test.
Understanding the Specific Sample Requirement
The most common misconception about the FIT is needing a large amount of stool for analysis. Unlike older chemical tests that needed a bulk specimen, the FIT detects blood at a molecular level, relying on antibodies to target human hemoglobin. This process requires only enough material to cover the specialized collection device.
Each FIT kit contains a sampling wand or stick attached to the cap of the collection tube. You only need to gently scrape the surface of the stool until the grooves or dimples on the tip of the stick are completely covered. This small amount ensures the correct ratio of stool to the liquid preservative inside the tube. Adding an excessive amount of stool can lead to the sample being rejected by the laboratory, as it may interfere with the testing mechanism.
Step-by-Step Guide to Accurate Collection
The collection process begins by preparing the environment to ensure the stool remains uncontaminated. Since the stool must not touch the toilet water, you need a method to catch the sample, such as using the collection paper provided in the kit. Alternatively, you can use a clean, dry container or place several layers of toilet paper across the bowl to create a sling. It is important to urinate and flush the toilet before having a bowel movement to eliminate any water or cleaner residue that could affect the sample.
Once the stool is safely collected, open the FIT tube and remove the collection stick attached to the cap. Gently scrape the tip of the stick across the surface of the stool until the grooves or dimples are completely covered. Do not fully insert the stick into the center of the stool, as the surface is where bleeding is most likely to be detected. After sampling, carefully insert the stick back into the tube and twist the cap tightly until it seals securely.
The final steps involve labeling and preparing the sample for transport. Write the date and time of collection clearly on the tube label, as this information is necessary for the laboratory. Place the sealed collection tube into the provided biohazard bag and then into the return envelope or box. Return the sample as quickly as possible to the designated lab or clinic according to the kit instructions to preserve its integrity.
Common Errors That Affect Test Results
Factors beyond the sample quantity can compromise FIT results. The most common error is contamination, which occurs when the stool contacts toilet water, urine, or chemicals from the toilet bowl. Since the test is highly sensitive, even residual water or cleaning agents can interfere with the analysis. Taking the sample while experiencing active bleeding from hemorrhoids, anal fissures, or menstruation can also lead to a false positive result.
Logistical errors related to timing and storage are also frequent causes for sample rejection. The sample must be returned to the lab within a specific timeframe, often within seven days of collection, to ensure the stability of the hemoglobin. Improper storage, such as freezing the sample or exposing it to high temperatures, can render it unusable. Incomplete or inaccurate labeling, such as failing to write the date and time of collection, prevents the lab from processing the specimen.