Result card

  • SAF7: What are the special features in using (applying/interpreting/maintaining) FIT that may increase the risk of harmful events?

What are the special features in using (applying/interpreting/maintaining) FIT that may increase the risk of harmful events?

Authors: Agnes Männik, Irena Guzina, Petra Jandova, Leonor Varela Lema, Gerardo Atienza Merino

Internal reviewers: Matthias Schwenkglenks, Ingrid Wilbacher

The domain literature search and additional search was used.

The risk of harmful events can be increased due to unexperienced laboratory personnel, who make mistakes, when reading test results{8}. There are many factors infuencing gFOBT test results – food, consumed medications, faecal hydration. FIT test, however does not have dietary or medications restrictions {13}.

  • [NHS Centre for Reviews and Dissemination : Diagnostic Accuracy and Cost-Effectiveness of Faecal Occult Blood Tests Used in Screening for Colorectal Cancer: A Systematic Review, 2007] {8}


The accuracy of FOBTs depends upon appropriate performance and interpretation of the test(s). Interpretation of FOBTs may be problematic when they are done by inexperienced personnel. In a retrospective review of questionnaires applied to accredited laboratory personnel (in order to determine their ability to interpret FOBT results), 12% were unable to correctly interpret sample test cards (mainly false-positive results). This finding raised concerns that people with detectable colorectal cancers may be missed, solely because of errors in interpretation. One suggestion to improve test interpretation is the use of tests with automated reading. Alternatively a centralised location for the collection, processing, and interpretation of all tests would facilitate measures to improve consistency.


Guaiac tests are generally best at detecting large, more distal lesions. Because they depend upon peroxidase or pseudo-peroxidase activity in the faeces, and are not specific to the pseudoperoxidase activity of human haemoglobin, many variables are said to influence their results. These include dietary factors, for example animal haemoglobin/myoglobin in red meat, fruits and vegetables high in peroxidase activity (false-positive results), high doses of vitamin C (false-negative results), aspirin or other medication that may cause gastrointestinal bleeding (false-positive results) and faecal hydration. The drying out of the faecal specimen and exposure to high ambient temperature can also result in false negative findings. Conversely rehydration of the sample may deactivate the peroxidases from fruit and vegetables reducing the number of false positive results. A systematic review of five RCTs of CRC screening using a guaiac test (Haemoccult) suggested that dietary restriction during unrehydrated FOBT may not be necessary as it did not appear to affect positivity rates and completion rates. However, the review did not include evidence on the use of more recent guaiac tests such as Haemoccult Sensa, which are believed to be more susceptible to the effects of diet. It also failed to account for dietary differences between countries and ethnic groups

Complications from colonoscopy may depend on the education and experience of health professional {13}.

The risk of harmful events may be increased due to unexperienced laboratory personnel, dietary and medication restrictions (gFOBT) and education and experience of health professionals.

Männik A et al. Result Card SAF7 In: Männik A et al. Safety In: Jefferson T, Cerbo M, Vicari N [eds.]. Fecal Immunochemical Test (FIT ) versus guaiac-based fecal occult blood test (FOBT) for colorectal cancer screening [Core HTA], Agenas - Agenzia nazionale per i servizi sanitari regionali; 2014. [cited 3 December 2022]. Available from: