Category: Cancer Screening
FIT Test (Faecal Immunochemical Test)
Also known as: FIT · Faecal immunochemical test · Immunochemical FOBT
A FIT test, or faecal immunochemical test, is a stool test that looks for small amounts of human blood that are not visible to the eye. Hidden blood can come from bowel polyps or bowel cancer, so FIT is used to screen for colorectal cancer in people who have no symptoms. The sample is collected at home and sent to a laboratory. A positive FIT does not mean cancer is present: it means a colonoscopy is needed to find out what caused the bleeding.
How a FIT test works
Polyps and cancers in the colon or rectum can bleed in amounts far too small to see. A FIT test detects that hidden blood. Specifically, immunochemical faecal occult blood tests detect human haemoglobin from partially digested blood in the stool.
You collect the sample at home and send it by post to be tested, which is a large part of why FIT works as a population screening test. It is quick, private and needs no preparation.
FIT versus older stool blood tests
FIT replaced an older generation of guaiac-based faecal occult blood tests. Immunochemical tests are more sensitive and more specific than the guaiac-based tests used in the past, and they do not require dietary restriction.
Because FIT is specific to human haemoglobin, food and most medicines do not interfere with the result in the way they could with older tests.
Who should have a FIT test, and how often
Colorectal cancer screening matters a great deal in Singapore: approximately 1,200 new cases are diagnosed each year, making it the most common cancer in Singapore. Screening should begin at age 50 for individuals without risk factors, and earlier for those at increased risk. Subsidised screening is available under Healthier SG Screening.
Frequency differs by country. In Singapore, individuals with a negative result are tested annually. In the UK, bowel cancer screening is offered to people aged 50 to 74 every 2 years. US guidance recommends most people begin colorectal cancer screening at age 45.
What a positive FIT result means
A positive FIT means human blood was detected in the sample. Blood can come from causes other than cancer, including haemorrhoids and polyps, so a positive result is a reason to investigate, not a diagnosis. Individuals with a positive FOBT require colonoscopy, which allows the bowel to be examined directly and any polyps to be removed.
Finding polyps early is the point of the exercise. Most colorectal cancers arise from adenomatous polyps, and that transformation takes 5 to 10 years, so removing a polyp can prevent a cancer from ever forming.
The limits of a FIT test
FIT is a screening test, not a diagnostic one, and a negative result does not completely rule out colorectal cancer. Its main weakness is sensitivity: an estimated 50% of cancers will be missed on each screening round, which is why FIT must be done annually in the Singapore recommendation. Repeating the test on schedule is what makes the programme effective, not any single result.
FIT also only detects bleeding. A polyp or cancer that is not bleeding at the time you collect the sample will not be picked up.
Most importantly, screening is for people without symptoms. If you have rectal bleeding, a persistent change in bowel habit, unexplained weight loss or abdominal pain, see a healthcare professional rather than relying on a screening test.
FIT and stool DNA testing
FIT and stool DNA testing are different approaches to the same problem. FIT looks for blood. A stool DNA test analyses DNA from cells shed into stool for selected molecular changes associated with abnormalities in the colon or rectum.
Each has its own advantages and limitations, and neither replaces colonoscopy where that is what a result calls for.
Frequently asked questions
Does a positive FIT test mean I have cancer?
No. A positive FIT means human blood was found in the sample. Blood can come from causes other than cancer, including haemorrhoids and polyps. A positive result means a colonoscopy is recommended to find out what caused the bleeding.
Do I need to change my diet before a FIT test?
No. Immunochemical tests detect human haemoglobin specifically, so dietary restriction is not required. This is one of the advantages FIT has over the older guaiac-based faecal occult blood tests.
How often should I do a FIT test?
It depends on the national programme. In Singapore, people with a negative result are tested annually from age 50. In the UK, bowel cancer screening is offered every 2 years to people aged 50 to 74.
What is the difference between a FIT test and a colonoscopy?
A FIT test is a stool sample collected at home that looks for hidden blood. A colonoscopy is a procedure in which a healthcare professional examines the inside of the colon and rectum directly with a camera, and can remove polyps during the same procedure. A positive FIT is normally followed by a colonoscopy.
Can a FIT test miss bowel cancer?
Yes. An estimated 50% of cancers are missed on each screening round, which is why the test is repeated on a schedule rather than relied on once. A negative FIT does not completely rule out colorectal cancer, and it is not a substitute for seeing a doctor about symptoms.
Related terms
Related Camtech Health tests
References
Understanding your health information
Our glossary is designed to help make health and testing terminology easier to understand.
The information provided here is for general educational purposes only and should not replace professional medical advice, diagnosis or treatment. The purpose and regulatory status of individual Camtech Health tests may differ depending on the product and country in which they are supplied.
If you have symptoms, receive an unexpected result or are concerned about your health, speak with an appropriately qualified healthcare professional.
