Occult gastrointestinal bleeding is defined as bleeding which is unknown to the person. It can be caused by several different reasons and it is important to understand that occult blood in faeces does not automatically mean that the reason would be malignant. Therefore, if a FOB test is positive, further investigations should be performed to identify the source of bleeding.
Immunochemical faecal occult blood tests (iFOBTs, FITs) exist both as qualitative and quantitative. The qualitative iFOBTs can be visually interpreted whereas the quantitative tests are often instrument-read and have thus enhanced quality while eliminating the potential for visual bias by the observer (1).
The iFOBTs use antibodies to detect the human occult blood and should therefore not be subject to interference from dietary blood (2). The iFOBTs are rapidly replacing the guaiac-based FOB tests (gFOBTs) because of their many advantages. These include greater clinical and analytical sensitivity (3, 4), collection of a single screening sample (5, 6–8), simple and hygienic sampling devices (5), higher specificity for lower gastrointestinal tract bleeding (9, 10, 11), and no dietary restrictions prior to or during sampling for iFOBTs (1, 5). Use of iFOBTs result in improved clinical performance and higher participation rates in screenings (4, 12, 13). Compared to gFOBTs, iFOBTs might, however, require a larger initial investment and have slightly weaker sample stability after collection (2, 4, 14, 15, 16).
Even though iFOBTs are not as widely evaluated as traditional gFOBTs, adequate population-based comparative studies have been made (4). Overall, the sensitivity of iFOBTs for CRC is stated to be 61−91% and the specificity 91−98% (17). iFOBTs enable detection of Hb in faeces at lower concentrations than gFOBTs, and therefore increase clinical sensitivity by detecting small or intermittently bleeding lesions (2).
Adequate clinical sensitivity and specificity for screening can be obtained using a single iFOBT test per subject (2, 6, 7). Likely due to the improved clinical performance, the use of only one or two samples and simpler sample collection and handling techniques (4), screening programmes with iFOBTs has been shown to have a participation rate higher than gFOBTs (12, 13).
Even though gFOBTs are more affordable than iFOBTs, studies have shown that use of iFOBTs is a more cost-effective strategy in CRC screening (18–20). This is likely due to the increased sensitivity of the tests as well as the higher participation rate (4). The higher test costs are also balanced by use of automated analysers that lead to reduced staff costs, and by the need of performing fewer tests per patient (2). Cost-analyses do, however, need to be made separately in each country, as e.g. test and personnel costs, logistics and preferences of screening vary (4).
Adjustable cut-off concentration and risk stratification
The most prominent advantage of a quantitative FOB test is that the user can select the cut-off concentration in order to decide on further investigation (1). This means that the analytical sensitivity of the test can be adjusted according to e.g. screening settings, national guidelines or local requirements (1, 3). The goal with choosing a cut-off concentration is to provide an adequate positivity rate with acceptable trade-off between detection rate and unnecessary colonoscopies performed. The choice depends on the test device, sampling, number of samples used, intended detection rate, prevalence of CRC in population, and political issues such as availability of colonoscopy (2, 21).
Knowing the total amount of Hb in the faecal mass enables comparison of FOB results obtained with different methods. Test manufacturers use various sampling devices and buffers, collect various masses of faeces and report Hb concentrations in different ways. Therefore FOB results expressed in ng Hb/ml buffer are not comparable between different methods (22). A suggestion on standardisation of units for reporting faecal Hb concentrations has been made (23). The only unit that allows comparison of FOB results between test devices and across clinical studies is μg Hb/g faeces. The unit can be calculated if the dilution ratio of the sample is known, but sophisticated automated iFOBTs provide the user with results expressed in μg/g automatically. (2)
Occult bleeding increases gradually with growing size of polyps and advancing stage of CRC, and FOB tests can potentially detect both CRC and its preliminary stages (6, 24, 25). Irregular bleeding patterns and rates (27) as well as many other factors may cause varying faecal Hb concentrations. Qualitative tests indicating only that the result is positive, do not give any information on the amount of occult bleeding. Risk stratification based on the exact numerical Hb concentration might help clinicians in identifying subjects with alarmingly high FOB concentrations who should undergo further examinations immediately. The interval between screen-detected disease and the start of definitive management is an unpleasant time for the patient and presents an opportunity for disease progression (3, 26).
The most common techniques for further investigations include colonoscopy, flexible sigmoidoscopy, air-contrast barium enema, molecular markers, virtual colonoscopy or colon capsule endoscopy (5, 11). Colonoscopy is considered the most effective visualisation technique to detect CRC and high-risk adenomas (4), and the recommended method to evaluate the colon in patients with increased FOB concentrations (11).
QuikRead go is not registered in the USA.
Published May 4, 2016
1. Fraser CG et al. Newer Fecal Tests: Opportunities for Professionals in Laboratory Medicine. Clin Chem. 2012;58(6):963−5.
2. Halloran, SP et al. European guidelines for quality assurance in colorectal cancer screening and diagnosis. First Edition. Faecal occult blood testing. Endoscopy. 2012;44:1−23.
3. von Karsa, L et al. European guidelines for quality assurance in colorectal cancer screening and diagnosis: Overview and introduction to the full Supplement publication. Endoscopy. 2013;45:51−9.
4. Duffy, MJ et al. Use of faecal markers in screening for colorectal neoplasia: a European Group on Tumor Markers (EGTM) position paper. Int J Cancer. 2011;128:3−11.
5. Seifert B. Colorectal Cancer Screening. Prague: Maxdorf Publishing; 2013.
6. Kovarova, JT et al. Improvements in colorectal cancer screening programmes - quantitative immunochemical faecal occult blood testing - how to set the cut-off for a particular population. BiomedPap Med Fac Univ Palacky Olomouc Czech Repub. June 2012;156(2):143−50.
7. Castiglione, G et al. Basic variables at different positivity thresholds of a quantitative immunochemical test for faecal occult blood. J Med Screen. 2002;9(3):99−103.
8. Fenochi, E et al. Screening for colorectal cancer in Uruguay with an immunochemical faecal occult blood test. Eur J Cancer Prev. 2006;15:384−90.
9. Ahlquist, DA. et al. Fecal blood levels in health and disease. A study using HemoQuant. N Engl J Med. 1985;312:1422−8.
10. Rockey, DC et al. Detection of upper gastrointestinal blood with fecal occult blood tests. Am J Gastroenterol. 1999;94:344−50.
11. Rockey, DC. Occult Gastrointestinal bleeding. N Engl J Med. June 1999;341(1):38−46.
12. van Rossum, LG et al. Random comparison of guaiac and immunochemical fecal occult blood tests for colorectal cancer in a screening population. Gastroenterology. 2008;135:82−90.
13. Hol, L et al. Screening for colorectal cancer; randomised trial comparing guaiac-based and immunochemical faecal occult blood testing and flexible sigmoidoscopy. Gut. 2010;59:62−8.
14. European Union. European guidelines for quality assurance in colorectal cancer screening and diagnosis. 1st ed. Luxembourg: Publications Office of the European Union; 2010.
15. van Rossum, LG et al. False negative fecal occult blood tests due to delayed sample return in colorectal cancer screening. Int J Cancer. 2009;125:746−50.
16. Brown L, Fraser C. Effect of delay in sampling on haemoglobin determined by faecal immunochemical tests. Ann Clin Biochem. 2008;45:604−5.
17. Ehitlock, EP et al. Screening for colorectal cancer: a targeted. updated systematic review for the U.S. preventive services task force. Ann Int Med. 2008;149:638−58.
18. Berchi, C et al. Cost-effectiveness analysis of two strategies for mass screening for colorectal cancer in France. Health Econ. 2004;13:227−38.
19. Berchi, C et al. Cost-effectiveness analysis of the optimal threshold of an automated immunochemical test for colorectal cancer screening. Int J Technol Assess Health Care. 2010;26:48−53.
20. Grazzini, G. et al. Cost evaluation in a colorectal cancer screening programme by faecal occult blood test in the District of Florence. J Med Screen. 2008;15:175−81.
21. van Rossum, LG et al. Cut-off value determines the performance of a semi-quantitative immunochemical faecal occult blood test in a colorectal cancer screening programme. Br J Cancer. October2009;101(8):1274−81.
22. Allison, JE et al. Comparing Fecal Immunochemical Tests: Improved Standardization Is Needed. Gastroenterology. 2012;142:422−31.
23. Fraser, CG. A Proposal to Standardize Reporting Units or Fecal Immunochemical Tests for Hemoglobin. JNCI. June 2012;104(11):810−4.
24. Winawer, SJ et al. Colorectal Cancer Screening: Clinical Guidelines and Rationale. Gastroenterology. 1997;112:594−642.
25. Digby, J et al. Faecal haemoglobin concentration is related to severity of colorectal neoplasia. J Clin Pathol. 2013;66:415−9.
26. NHS Quality Improvement Scotland. Bowel Screening Programme. Clinical Standards February 2007. 2007. Available at: http://www.bowelscreening.scot.nhs.uk/wp-content/uploads/2007/06/bowelsc_stnf_feb07.pdf. Accessed December 11, 2013.
27. Ahlquist, DA et al. Patterns of occult bleeding in asymptomatic colorectal cancer. Cancer. 1989;63:1826−30.
This summary is intended to provide healthcare practitioners with an overview of QuikRead go iFOBT and QuikRead FOB quantitative, as well as the diagnostic potential of immunochemicalFaecal Occult Blood tests.Although every effort has been made to provide accurate information, Orion Diagnostica accepts no responsibility whatsoever for the accuracy, correctness or completeness of the informationcontained in this booklet. It is the responsibility of the healthcare practitioner to evaluate the contents of this booklet and to verify the information presented. The ultimate judgment regardingthe care and appropriate treatment of a particular individual must always be made by the healthcare practitioner in the light of all the clinical information available about the individual.Orion Diagnostica therefore accepts no liability for any injury or damage to person or property resulting from acceptance of the information in this booklet. Hence, liability claims regardingpossible injury or damage will be rejected.The information in this summary may contain references to products that are not available or approved by the regulatory authorities in your country. Orion Diagnostica assumes no responsibilityfor you accessing information that may not comply with legislation, regulations or usage applicable in your country. You are advised to consult Orion Diagnostica’s local business contactor marketing partner for information about the availability of Orion Diagnostica products in your country.