Early detection of colorectal cancer with a fecal occult blood test (FOBT)

This fact box will help you to weigh the benefits and harms of early detection of colorectal cancer with a fecal occult blood test (FOBT). The information and numbers are based on the best scientific evidence currently available.

This fact box was developed by the Harding Center for Risk Literacy.

What is colorectal cancer?

Colorectal cancer occurs in the inner wall of the large intestine and usually starts with precancerous lesions (polyps). Polyps are benign growths of tissue in the mucous membrane of the large intestine that may grow into colorectal cancer.

What is early detection of colorectal cancer with a fecal occult blood test (FOBT)?

Early detection (screening) targets people who do not show symptoms of a particular disease (here, colorectal cancer). The aim is to detect and treat colorectal cancer earlier.

The fecal occult blood test is used to examine stool samples in order to detect minute quantities of blood that are invisible (occult) to the human eye. Blood in the stool may be a sign of colorectal cancer. However, the test does not indicate the source of bleeding. A positive test implies a higher probability of colorectal cancer. In these cases, a colonoscopy is usually performed for clarification.

Who might consider a fecal occult blood test?

The fecal occult blood test is covered by statutory health insurance for men and women aged 50 years and older in Germany [2].

What are the alternative treatment options?

Other screening tests for colorectal cancer include flexible sigmoidoscopy and colonoscopy. Colonoscopies are covered by statutory health insurance for people aged 55 years and older in Germany [2].


What does the fact box show?

The fact box shows the benefits and harms of screening with FOBT for people aged 45 years and older who either did or did not participate in screening.

The table may be read as follows:

7 out of every 1,000 people without screening died from colorectal cancer over a period of 9 to 30 years. In the same time period, 6 out of every 1,000 people with screening died from colorectal cancer.

The numbers in the fact box are rounded. The numbers on colorectal cancer mortality are based on four studies with about 310,000 participants. The numbers on the diagnoses are based on two studies with about 220,000 participants. The numbers on the harms are based on two studies with about 21,000 participants for false-positive test results, and on three studies with about 3,200 participants for false-negative test results [1].

What other aspects should be considered?

Screening did not affect the total number of deaths when all potential causes of death are considered. About 244 out of every 1,000 people died overall, independent of whether they were screened. This means that the studies showed no evidence of FOBT saving one life over a time period of 9 to 30 years.

Data on the occult blood test are based on studies about the effect of the guaiac-based fecal occult blood test (gFOBT). Since January 1, 2017, the gFOBT has been replaced by the immunological fecal occult blood test (iFOBT or FIT). At present, there are no systematic reviews of studies on the iFOBT that report patient-relevant outcomes. First results from currently running long-term studies are expected in 2026.

The iFOBT is assumed to have benefits similar to the gFOBT or even greater [3].

Do the results provide proof (evidence) for the benefits and harms of the screening by fecal occult blood test?

Overall the evidence is of low to medium quality:

It is likely that further research will change the results on cancer specific mortality and the diagnosis of advanced colorectal cancer (moderate evidence).

It is very likely that the results of the false alarms (false positive results) and the false negative results will be changed by further research (low evidence).

Last update

November 2016


Information in the fact box was obtained from the following sources:

[1] Fitzpatrick-Lewis D, Ali MU, Warren R, et al. Screening for colorectal cancer: a systematic review and meta-analysis. Clin Colorectal Cancer 2016 doi: 10.1016/j.clcc.2016.03.003.

[2] Gemeinsamer Bundesausschuss. Früherkennungsuntersuchungen im Überblick 2016. Available from: www.g-ba.de.

[3] Institut für Qualität und Wirtschaftlichkeit im Gesundheitswesen. Einladungsschreiben und Entscheidungshilfen zum Darmkrebs-Screening: Abschlussbericht; Auftrag P15-01. 24.10.2016. (IQWiG-Berichte; Band 451). Available from: www.iqwig.de.

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The idea of fact boxes was developed by Lisa Schwartz and Steven Woloshin. In several studies they demonstrated that fact boxes were effective tools for informing the general public about benefits and harms of medical interventions. Read more in the overview.


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