Exploring the science behind quantitative fecal immunochemical tests and their impact on colorectal cancer screening
Colorectal cancer (CRC) ranks as the third most commonly diagnosed cancer worldwide with approximately 1.4 million new cases and 700,000 deaths annually .
When identified at its earliest, localized stage, colorectal cancer has a 90% survival rate—a figure that plummets to just 10% once it has metastasized to distant organs 3 .
The original fecal occult blood test (FOBT) used a chemical called guaiac, derived from wood resin of Guaiacum trees 5 .
Despite limitations, gFOBT reduced CRC mortality by 14% according to a meta-analysis of 19 studies 1 .
The fecal immunochemical test (FIT) uses antibodies specifically designed to target the globin protein in human hemoglobin 1 3 .
FIT demonstrates 70-85% sensitivity for detecting colorectal cancer, compared to 50-70% for gFOBT 1 .
| Parameter | gFOBT | FIT | FIT-DNA (Cologuard) |
|---|---|---|---|
| Target | Heme component of hemoglobin | Human globin protein | Hemoglobin + DNA markers |
| CRC Sensitivity | 50-70% | 70-85% | ~92% |
| Advanced Adenoma Sensitivity | 10-30% | 25-40% | ~43% |
| Dietary Restrictions | Required | Not needed | Not needed |
| Sample Collection | 3 consecutive stools | 1 stool sample | 1 stool sample |
| Specificity | 85-95% | 90-95% | 87-90% |
A groundbreaking German study conducted as part of the BliTz study set out to evaluate the stability of hemoglobin measurements across ten different quantitative FIT systems .
Twenty randomly selected stool samples were chosen from participants in the German screening colonoscopy program, with initial hemoglobin concentrations ranging from 10-100 μg/g .
For each FIT system, samples were stored at three different temperatures (5°C, 20°C, and 35°C) to simulate refrigerator, room, and warm summer conditions .
Measurements were taken after 1, 4, 5, and 7 days to observe how hemoglobin levels changed over time .
Three sampling devices of each manufacturer were filled with each stool sample, ensuring statistical reliability .
This systematic approach allowed the researchers to directly compare the stability performance of different FIT brands under identical conditions—the first study of its kind to do so.
At 5°C, almost all FITs showed fairly stable results throughout the 7-day observation period, with minimal decay in hemoglobin concentrations .
At 20°C, most FITs remained stable for up to 4 days, but began showing significant declines in positivity rates thereafter .
At 35°C, positivity rates significantly declined from day 4 onward for most FITs, potentially leading to false negative results .
| Storage Temperature | Stability Duration | Impact on Positivity Rates | Recommendations for Screening Programs |
|---|---|---|---|
| 5°C (Refrigeration) | 7 days with minimal decay | Less than 5% decline | Ideal for program logistics; samples remain reliable for weekly pickups |
| 20°C (Room Temperature) | 4 days of stability | Significant decline after day 4 | Samples should reach lab within 3-4 days during moderate weather |
| 35°C (Summer Heat) | Rapid decay after day 2 | Major declines from day 4 | Special precautions needed in warm climates; expedited transport recommended |
The implications of these findings were immediate and practical: FIT-based screening programs needed to consider both ambient temperature and time between sampling and analysis to maintain test accuracy. This was particularly important for programs serving remote or rural areas where transport times might be longer .
Conducting rigorous FIT evaluation requires specialized materials and reagents. The German stability study utilized a comprehensive array of tools to ensure accurate, reproducible results .
| Tool Category | Specific Examples | Function in Research |
|---|---|---|
| Quantitative FIT Systems | OC Sensor, FOB Gold, QuikRead go iFOBT | Provide standardized measurement of fecal hemoglobin concentrations using immunoturbidimetric or immunoassay principles |
| Fecal Sampling Devices | Manufacturer-specific vials with stabilizing buffers | Collect defined stool amounts (typically 10-40 mg) while preserving hemoglobin integrity during storage |
| Analytical Instruments | OC Sensor io, Eurolyser CUBE, Dynex DSX | Automatically measure hemoglobin concentrations, eliminating subjective interpretation bias |
| Temperature Control Systems | Refrigerated incubators, temperature-monitored storage | Simulate various environmental conditions to evaluate sample stability |
| Sample Processing Tools | Vortex mixers, homogenization equipment | Ensure even distribution of stool in stabilizing buffers for consistent measurements |
| Quality Control Materials | Calibrators, control samples with known hemoglobin concentrations | Verify analytical performance and measurement accuracy across testing systems |
The sophisticated design of fecal sampling devices deserves special attention. These are not simple containers—each manufacturer's device contains a brand-specific hemoglobin-stabilizing buffer and a plastic stick that collects a precisely defined amount of stool (typically 10-40 mg). When the stick is inserted back into the vial, a tight entrance removes excess stool, ensuring consistent sample sizes across tests—a crucial factor in obtaining reliable quantitative results .
While FIT represents a significant advancement in non-invasive colorectal cancer screening, research continues to push boundaries. Scientists are exploring several promising avenues:
Researchers are developing blood tests that detect methylated DNA sequences, such as the Septin-9 gene. While current versions have relatively low sensitivity for advanced adenomas (around 11-15%), they offer the potential to improve screening participation among those reluctant to provide stool samples 2 .
Cutting-edge proteomic research has identified promising new stool biomarkers beyond hemoglobin. One particularly exciting candidate is fibrinogen, which demonstrated a diagnostic accuracy of 86% for advanced adenomas in preliminary studies—far surpassing FIT's performance for detecting these precancerous lesions 6 .
Researchers are developing compact, quantitative FIT biosensor platforms that could be used in low-resource settings. These label-free devices use interdigitated electrode sensors to detect hemoglobin concentrations as low as 10 μg/g feces—comparable to laboratory-based systems but at a fraction of the cost and size 3 .
The quantitative fecal immunochemical test represents more than just technological progress—it embodies a shift toward patient-friendly, accurate, and accessible preventive healthcare.
By detecting invisible traces of blood with remarkable precision, this unassuming test serves as a vital early warning system for one of humanity's most common cancers. The meticulous research into FIT stability and performance exemplifies how evidence-based medicine continuously refines our tools for disease prevention. As we look to the future, the ongoing innovation in biomarker research and testing technology promises to further transform our approach to colorectal cancer—moving from treatment of advanced disease to prevention and early interception.
What makes FIT truly remarkable is its ability to make sophisticated diagnostics accessible to millions. In the quiet simplicity of a stool sample lies the power to detect cancer early, save lives, and give families more time with their loved ones—a testament to how medical innovation, however complex its underpinnings, ultimately serves humanity in the most personal of ways.