Intestinal physiological bleeding is considered to be within 0.5 - 1.0 ml per day and, in such cases, the FOB test shows a negative result.
If the bleeding is higher and the FOB test shows a positive result, a more thorough investigation - usually a colonoscopy - is required in order to clarify the origin of the bleeding. To compare the quantitative FOB results, the sample dilution must be standardised. The QuikRead FOB sampling tube regulates the amount of stool sample (10 mg) in 2 ml of buffer resulting in a 1:200 dilution.
The immunological, latex-enhanced method reacts only with human globin, thus eliminating the need for dietary restrictions prior to sampling.
The European Group on Tumor Markers (EGTM) recommends the use of quantitative, immunological FOB testing which enables the cut-off value to be set by the clinician.
The American Gastroenterological Association recommends that persons at average risk (asymptomatic, age > 50 years, no other risk factors) should be tested for FOB annually.1 Pharmaceuticals causing gastrointestinal irritation, such as nonsteroidal anti-inflammatory drugs, should be avoided during the test period since they may cause bleeding.1 This may lead to unnecessary further tests.
Immunological FOB tests (iFOBT) have enabled a significant improvement in analytical specificity.2
References
1. Winawer SJ, Fletcher RH, Miller L, Godlee F, Stolar MH, Mulrow CD, Woolf SH, Glick SN, Ganiats TG, Bond JH, Rosen L, Zapka JG, Olsen SJ, Gardello FM, Sisk JE, van Antwerp R, Brown-Davies C, Marciniak DA, Mayer RJ: Colorectal cancer screening: Guidelines and rationale; Gastroenterology 1997; 112: 594 - 642.
2. European Guidelines for Quality Assurance in Colorectal Cancer Screening and Diagnosis, European Union 2010.