OnSite FOB Rapid Test
Hemoglobin VariantsHemoglobin variants are a part of the normal embryonic and fetal development, but may also be pathologic mutant forms of hemoglobin in a population Function Hemoglobin A (22) The most common with a normal amount over 95%Hemoglobin S (2S2) A variant form of hemoglobin found in people with sickle cell disease, not uncommon in USA Hemoglobin H (4) A variant form of hemoglobin, formed by a tetramer of chains, which may be present in variants of thalassemia. ..
Benefit of FOB Detection Detection of gastrointestinal (GI) bleeding facilitates early diagnosis of GI track cancer
FOB testing is recommended annually by the American Cancer Society (2001) for average-risk women and men, 50 years of age and older. However, patients with significant risk factors such as family history of colorectal cancer should be screened earlier and more often.
Methods Biochemical method -Guaiac False positive guaiac results may occur from a diet of red or rare meats and/or dietary peroxidases. Vitamin C (ascorbic acid) may cause false negative results. Fecal Hb detection - Immunological May fail to detect upper gastrointestinal tract bleeding, producing a false negative result Mabs recognize single antigenic determinants and may not react positively with genetic variants of human hemoglobin, such as occur in sickle cell disease
Analytical Performance Characteristics Sensitivity of Immunological Tests to Hemoglobin VariantsMabs equivalently recognizes variants of hemoglobin (e.g., hemoglobin SS and hemoglobin CC) in whole blood samples from persons with hemoglobinopathies that are prevalent in the United States Interference Hemoglobin from beef, chicken, fish, horse, pig, rabbit, goat, and sheep Myoglobin or ground up meat extracts prepared from beef, chicken, fish, horse, pork or ham, rabbit, goat, and sheep Cut-off Reproducibility (Qualitative Tests) Prozone (Hook) Effect (Immunological Tests) Stability Test kit stability Specimen collection and handling Quality Control
Analytic Sensitivity 200 ng/ml : low false positive 50 ng/ml : intermediate sensitivity 25 ng/ml : high sensitive, high positivity rate
Factors Impact Test Performance Representative fecal sampleCause False negative Solution: Randomly in 5-6 spots Too much fecal matters picked up No flow migration Solution: Sample limiting device and warning
Results are not conclusive evidence of the presence or absence of gastrointestinal bleeding or pathology.
Test results can only be regarded as a preliminary screening or as an aid to diagnosis. It is not intended to replace other diagnostic procedures such as colonoscopy, sigmoidoscopy, or other x-ray studies.
Because gastrointestinal lesions may bleed intermittently and blood in feces is not distributed uniformly, a negative test result does not assure absence of lesions.
Any positive result should be followed up with further studies to establish the source of bleeding.
Limitations Hemoglobin protein tends to be altered chemically as it passes through the GI tract, changing its antigenicity. A test may detect occult blood when it is the result of lower gastrointestinal tract bleeding, but may fail to detect upper gastrointestinal tract bleeding, producing a false negative result.
Risk to Health Failure of an FOB test to perform as indicated, or error in interpretation of results, may lead to improper patient management, including misdiagnosis and inappropriate treatment. For example, false negative results from an FOB test in patients who have asymptomatic cancer, adenoma, or other conditions could potentially give false reassurance and cause a delay in reporting symptoms and thus delay initiating treatment. False positive results could lead to performing unnecessary procedures (e.g., colonoscopy).
Conditions that are known to lead to false test results: Intermittent bleeding and irregular distribution of blood in the feces may contribute to false negative results.
Certain drugs such as aspirin and non-steroidal anti-inflammatory drugs may increase gastrointestinal bleeding and cause positive results. Iron compounds have been reported to cause false positive results. Ascorbic acid (vitamin C) taken at levels greater than 250 mg/day can cause false negative guaiac test results. Vitamin C in excess of 250 mg from either supplements or citrus fruits and juices should be avoided for three days before testing (Reference1).
The American Cancer Society cautions that a single FOB test done during a digital rectal exam in the doctors office is not sufficient for screening. The risk of a false negative result is mitigated by performing three separate tests on three consecutive bowel movements.
CTK FOB Test Complaint Review11 complaints over 7 years: Too sensitive led to false positive (2 cases) 25 ng/ml test Test result was not consistent among different lots (1 case)Fecal extraction buffer leakage (Main complaints)
FOB Rapid Test Quality Requirement False positive is not good False negative is not goodRecognizes variants of hemoglobin (e.g., hemoglobin SS and hemoglobin CC) in whole blood samples from persons with hemoglobinopathies that are prevalent in the United States (e.g., sickle cell disease).
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