FIT Antibody
Description
Definition and Biochemical Basis
FIT antibodies are immunoglobulins designed to bind specifically to the globin moiety of human hemoglobin . Unlike older guaiac-based fecal tests (gFOBT), FIT antibodies do not cross-react with non-human hemoglobin (e.g., from dietary sources) or partially digested blood from the upper gastrointestinal tract . This specificity minimizes false positives caused by dietary factors or medications .
Key characteristics:
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Detection method: Immunoassays (e.g., immunochromatography, ELISA) quantify hemoglobin at concentrations as low as 15–20 µg Hb/g stool .
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Clinical purpose: Early detection of CRC, advanced adenomas, and polyps .
Mechanism of Action
FIT antibodies operate through antigen-antibody binding:
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Stool samples are mixed with a buffer to extract hemoglobin.
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Antibodies conjugated to enzymes or fluorescent markers bind to globin.
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Signal intensity correlates with hemoglobin concentration, measured via automated analyzers (e.g., OC Sensor DIANA) .
Advantages over gFOBT:
| Feature | FIT Antibody Test | gFOBT |
|---|---|---|
| Specificity | Human globin only | Detects plant peroxidases |
| Dietary restrictions | None | Required |
| Sensitivity for CRC | 73–87% | 23–33% |
Sensitivity and Specificity
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CRC detection: 92% sensitivity (92% true positive rate) in symptomatic populations .
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Advanced adenomas: 22–42% sensitivity, outperforming gFOBT (6–23%) .
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False negatives: 8% of CRC cases show Hb <10 µg/g due to non-bleeding tumors .
Positivity and Detection Rates
| Study Population | Positivity Rate | CRC Detection Rate | Advanced Adenoma Rate |
|---|---|---|---|
| Average-risk adults | 6.3% | 0.7% | 2.1% |
| Symptomatic patients | 8.5% | 1.2% | 3.4% |
Applications Beyond Screening
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Risk stratification: Quantitative FIT results (e.g., Hb >150 µg/g) correlate with higher likelihood of advanced neoplasia .
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Therapeutic monitoring: Used post-polypectomy to assess recurrence risk .
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Symptomatic assessment: Evaluates iron-deficiency anemia or bowel habit changes .
Limitations
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Temperature sensitivity: Hemoglobin degrades in high temperatures during mail transit, reducing test accuracy .
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Variable thresholds: Cutoff values (10–20 µg Hb/g) impact sensitivity/specificity trade-offs .
Advances in FIT Technology
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Second-generation FIT: Automated platforms (e.g., Polymedco OC Sensor) achieve 97% accuracy (98% sensitivity, 96% specificity) .
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Bispecific antibodies (BsAbs): Experimental FIT-Ig platforms (e.g., EMB-01) target dual biomarkers (EGFR/c-MET) to enhance tumor detection and therapy .
Future Directions
Product Specs
Constituents: 50% Glycerol, 0.01M PBS, pH 7.4
Target Background
FIT's Role in Iron Uptake and its Interactions with Other Genes
- FIT is a key regulator of iron uptake, affecting the expression of 34 genes in root and seedling samples, including 13 novel genes. PMID: 27716045
- FIT interacts with ZAT12, linking iron deficiency responses to oxidative stress responses. PMID: 26556796
- FIT, similar to the FER-like iron deficiency-induced transcription factor, directly or indirectly modulates the protein levels of specific genes under iron deficiency conditions. PMID: 25951126
- Nitric oxide acts as a signal promoting not only the activation of FIT but also its protein stability, independent of ethylene and nitric oxide's transcriptional control. PMID: 21972265
- bHLH100 and bHLH101 are critical regulators of iron-deficiency responses, functioning independently of the master regulator FIT. PMID: 22984573
- Iron deficiency leads to post-translational regulation of FIT, resulting in decreased protein stability through proteasome-dependent degradation. PMID: 21426424
- FIT1, the gene encoding a putative transcription factor, regulates iron uptake responses in *Arabidopsis thaliana*, suggesting a model where *FRO2* and *IRT1* are differentially regulated by FIT1. PMID: 15539473
- AtbHLH29 encodes a bHLH protein, a functional ortholog of the tomato *FER* gene, proposed to be a transcription factor involved in iron deficiency responses and iron uptake. PMID: 16117851
- At2g28160 in *Arabidopsis*, commonly referred to as FIT, stands for FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR. PMID: 17466530
- FIT, along with AtbHLH38 or AtbHLH39, forms a complex that directly regulates the transcription of *FRO2* and *IRT1*, the targets of these three transcription factors. PMID: 18268542
