The FOBT medical abbreviation stands for fecal occult blood test, a test that checks a stool sample for small amounts of blood you cannot see. Fecal means related to stool, and occult means hidden.
The test is best known as a screening tool for colorectal cancer, because some cancers and large polyps bleed a little from time to time. It is usually done at home with a kit, then mailed or dropped off at a lab. Below you will find the two main types, how the results are used, and the shorthand that goes with them in clinic notes.
At a glance
Stands for
Fecal occult blood testMain types
Guaiac based (gFOBT) and immunochemical (FIT)Written as
FOBT, gFOBT, iFOBT, FIT, stool guaiacUsed in
Primary care, colorectal cancer screening, gastroenterologyNext step if positive
Usually a colonoscopyDo not confuse with
Stool DNA test (looks for DNA changes plus blood) and BRBPR (visible blood)
What the FOBT medical abbreviation means in practice
Small amounts of blood can leak into the bowel from many sources: polyps, cancers, hemorrhoids, ulcers, inflamed bowel and more. That blood is often far too little to change the color of stool. An occult blood test picks up these traces. A positive result does not say where the blood came from or why, only that it is there, which is why a positive test leads to a closer look rather than a diagnosis.
Clinicians also use the general idea in the hospital, for example checking stool for blood when someone has low blood counts, though screening guidelines are built around home kits.
Guaiac tests versus FIT
| Feature | Guaiac based gFOBT | Immunochemical FIT |
|---|---|---|
| What it detects | Heme, part of blood, through a chemical reaction | Human hemoglobin protein using antibodies |
| Samples | Usually from three separate bowel movements | Often just one sample |
| Diet and medicine limits | Often asked to avoid red meat, some pain relievers and high dose vitamin C beforehand | Usually no diet limits |
| Best at detecting | Bleeding anywhere in the gut | Bleeding from the lower bowel |
Many health systems now prefer FIT because it is simpler to do and less affected by food. Some notes call FIT an iFOBT, meaning immunochemical FOBT. A combined stool DNA test is a separate option that looks for both blood and DNA changes shed by abnormal cells.
Screening schedule and who it is for
For adults at average risk, many guidelines include a yearly FIT or high sensitivity guaiac test as one way to screen for colorectal cancer, commonly starting at age 45. It is one choice among several, alongside colonoscopy and other tests, each with its own schedule. People with a strong family history, past polyps, inflammatory bowel disease or symptoms such as bleeding are usually steered toward colonoscopy instead. The right plan depends on personal risk, so it is worth discussing with a primary care clinician.
Reading FOBT results in a chart
A primary care note: "FIT returned positive. Discussed result, GI referral placed for diagnostic colonoscopy." The stool test found blood, and the next step is a camera exam of the colon by gastroenterology (GI).
A hospital note: "Stool guaiac negative, Hgb stable." A bedside guaiac test found no hidden blood, and the hemoglobin level is not falling.
A negative result means no blood was found in that sample. Because cancers and polyps bleed on and off, a single negative test is not a guarantee, which is why the test is repeated on schedule.
What can cause a positive result
Most positive results are not cancer. Hemorrhoids, small tears near the anus, polyps that are not cancer, inflamed bowel and stomach ulcers can all cause bleeding. With guaiac tests, red meat and certain foods or pain relievers can sometimes produce a false positive. On the other hand, a positive result should never be ignored or simply repeated, since the point of the test is to find the people who need a colonoscopy. Related bowel shorthand includes CRC for colorectal cancer and GIB for gastrointestinal bleeding.
Tips for collecting a good sample
Read the kit directions fully before starting, and keep the sample away from toilet water and urine if the kit asks you to. Label it with the date and return it within the time the kit allows, since old samples can give wrong results. People who are having a menstrual period or bleeding hemorrhoids are often told to wait. For other screening and lab terms, see the lab and screening abbreviations hub.
Whether a stool test is a good fit for you, and what to do after any result, is a conversation to have with your primary care clinician.
Frequently asked questions
What does occult mean in FOBT?
Occult means hidden. The test looks for blood in stool that is present in amounts too small to see.
Is FIT the same as FOBT?
FIT is one type of fecal occult blood test. It uses antibodies to detect human hemoglobin, while the older guaiac test uses a chemical reaction. Both look for hidden blood in stool.
Does a positive FOBT mean cancer?
No. Most positive results come from other causes such as hemorrhoids, polyps or inflammation. A colonoscopy is usually needed to find the source.
How often is an FOBT done for screening?
When used for routine colorectal cancer screening, FIT or a high sensitivity guaiac test is usually repeated every year. Your clinician can tell you which schedule fits your risk.