Fecal Occult Blood Test Results and Stool Sample Collection
As an experienced lab technician, I have ten concerns regarding fecal occult blood testing that I'd like to share. Through this, you can learn how to interpret test results and understand their meaning.
1. Low Awareness of FOB Testing
When a doctor orders a "fecal occult blood test," it's not as simple as just "checking the poop."
Thoughtful hospitals provide an instruction sheet explaining preparation (dietary restrictions), sampling method (minimize water contact), delivery of sample (timeliness), result interpretation (positive doesn't necessarily mean problems), and follow-up (positives may require confirmatory testing).
Yet clinicians, lab techs, nurses etc. still get asked: "How do I do this test? Can I skip it? ..." A lot of effort goes into this simple, inexpensive test.
FOBT detects small amounts of blood in stool from gastrointestinal bleeding when there are no visible abnormalities. It's commonly used to screen for colorectal cancer risk, lowering mortality by 10-30%. With its non-invasiveness, acceptability and low cost, guidelines strongly recommend it.
FOBT usage is insufficient in China. In recent decades, stomach and colorectal cancer incidence has risen steadily due to dietary and lifestyle changes. They are among China’s top 5 most common and deadliest cancers.
Consider completing routine screening every 2 years from age 50, or earlier for high-risk groups. Yet national screening participation remains low, meaning many cancers are caught at later stages with poorer prognosis. We have much ground to cover in test implementation, automation and additional marker adoption.
2. High Sample Volumes
You may wonder why I fear too many samples when awareness is low. Major hospitals like Peking Union Medical College Hospital can receive 200-300 samples per day! Testing takes 5-10 hours, reporting 1-2 hours. Two dedicated technicians are needed daily for high-quality FOBT services. There are often exceptions requiring retesting too. Applaud our hardworking lab staff!
3. Cautions With Dark Stools
Some resources claim dark tarry stools signify upper GI bleeding. Not necessarily! Real GI bleeds can overwhelm immunoassay detection ranges, even causing false negatives. Chemical tests rarely have this issue.
But don't rely solely on chemical tests either! Black stools can result from foods, iron supplements for anemia, bismuth compounds for stomach issues etc., risking false positive chemical test results.
4. Requests for Dual Testing
The rationale is sound: immunoassays mitigate false negatives, chemical tests mitigate interferences. Also, upper GI bleeds often have degraded RBCs, so immunoassays alone risk false negatives. Thus, immunoassays accurately detect blood while chemical tests semi-quantify levels. However, dual testing increases workload and costs. Combined test kits are still uncommon. Please understand our lab's predicament!
5. Concerns Over High Positivity
By positivity, I mean percentages, not detection rates. False positives contribute, as discussed regarding chemical test interferences.
Positivity must specify pertinent conditions like cancer, advanced adenomas, polyps, or any abnormality. Clinicians want high test specificity for serious pathologies like cancer and ulceration.
But FOBT simply detects blood, not tumors! Many benign conditions cause fecal blood:
✅Improper sampling e.g. menstruation
✅Trauma e.g. tears
If too many benign cases are referred, gastroenterologists experience alarm fatigue.
6. Concerns Over Low Positivity
Low positivity means fewer cases detected. Missed early-stage colorectal (and associated upper GI) cancers are unacceptable! But multiple studies show qualitative FOBT performance varies widely.
7. Specimen Collection Issues
Patients may unknowingly provide inadequate samples. Most FOBT kits require minimizing urine and water content!
8. Untimely Delivery
Hemoglobin degrades over time, increasing risk of false negatives from delayed analysis.
9. Result Interpretation Inquiries
After testing, patients have many questions:
- Does a positive mean colon cancer? What now?
- Why do my results differ between tests?
- Does the duck blood noodle soup affect results? (Fair question!)
- Why not test for transferrin?
- Do I have a KRAS mutation?
- Why aren't other markers tested?
- Can I skip colonoscopy?
10. Patient Non-Compliance
My greatest fear is patients unwilling to follow-up positive results or adhere to surveillance.
One negative doesn’t confer immunity. Positives often warrant confirmatory testing due to intermittent bleeding with ulcers vs. persistent bleeding with cancer. However, over 50% of positive patients failed to complete recommended colonoscopy within 12 months in one study.
In summary, FOBT remains an irreplaceable first-line colorectal cancer screening tool, but national screening participation is still lacking. Reasons include suboptimal guideline adoption and technology limitations. As a result, many cancers are diagnosed at later stages, which is very unfortunate.
FOBT screening has tremendous public health significance in China, but general understanding remains inadequate. Testing volumes will rise substantially in future, necessitating increased automation and quantitative methodology improvements. While hemoglobin is the well-established primary marker, rising interest in transferrin for upper GI bleeding warrants observation. Other markers like calprotectin and gene methylation levels have also been proposed. Much work lies ahead!
As a provider of point-of-care testing solutions, Mantacc offers the necessary stool collection kits to facilitate fecal occult blood screening. Our specimen collection devices are designed for simple, hygienic sampling to obtain high quality samples for analysis. By standardizing the collection methodology, we enable greater accuracy and reliability of downstream occult blood testing. Please reach out to learn more about how our innovative stool collection kits can aid your screening programs.
Click to View → Mantacc Stool Sample Collection Kit