Focal active colitis (FAC) is when a specific type of white blood cell enters tiny structures in the colon wall, causing inflammation. Various conditions can lead to FAC, such as Crohn’s disease.

Infectious colitis and irritable bowel syndrome (IBS) are other possible causes.

FAC is not a condition in its own right. It is a microscopic finding that doctors can observe using diagnostic tools. Diarrhea is the symptom that most often cooccurs with FAC, but sometimes, there are no symptoms. Treatment involves addressing the underlying cause.

Learn more about focal active colitis, including symptoms, causes, diagnosis, treatment, and when to call a doctor.

A paper cut out of the human intestines, including the colon, where focal active colitis can occur.Share on Pinterest
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FAC is when glands in the colon, known as crypts, become inflamed due to the infiltration of a specific type of white blood cell.

These crypts, which some doctors also call crypts of Lieberkühn, are present between the cells of the intestinal lining. When the white blood cells, or neutrophils, get between these cells or inside the crypts, it causes inflammation. This is known as cryptitis.

Neutrophils are responsible for killing harmful microbes. They are part of the immune system and the first cell type to reach areas of inflammation. The term “focal” means this inflammation is in a specific area, rather than being widespread.

Diarrhea is the most frequent symptom that can manifest alongside FAC. Unintentional weight loss may also appear.

However, sometimes there are no symptoms. A doctor may find FAC during a colonoscopy screening. Colonoscopies are tests in which a doctor inserts a tiny camera into the colon via the rectum to look for changes in the colon wall.

The causes of FAC are varied, and may include:

As the causes range in severity, FAC may or may not be cause for concern.

Doctors identify FAC via a microscopic exam. This involves undergoing a colonoscopy with a biopsy, which means they will take a small sample of tissue during the procedure. A laboratory then analyzes this tissue, which may reveal the presence of neutrophils in several adjoining crypts.

The results of the microscopic exam cannot indicate whether or not the cause of the FAC is concerning. Doctors may need to perform additional tests to find the cause.

Doctors do not treat FAC itself. Instead, they treat what is causing it.

Crohn’s disease

Treatment for Crohn’s disease can involve:

  • dietary changes to help reduce symptoms
  • medications to help manage inflammation
  • bowel rests, which include getting nutrition via liquids or an intravenous (IV) line to give the gut a chance to heal
  • surgery to remove part or all of the colon

Some researchers believe that disease-causing bacteria, or healthy bacteria that become pathogenic under certain conditions, could play a role in Crohn’s disease. A 2021 meta-analysis of previous studies found that antibiotic treatment greatly improved symptoms.


Treatment for IBS can involve:

Antibiotics can also be a treatment for IBS. This is because there is a link between IBS and dysbiosis, or imbalanced gut bacteria. People with IBS are also more likely to have too much bacteria in their small intestine, which is a condition known as small intestinal bacterial overgrowth (SIBO).

One of the treatment approaches for SIBO and dysbiosis is antibiotics.

Infectious colitis

Not every person with infectious colitis requires treatment, as it can resolve on its own. However, antibiotics are necessary in some cases where there is a bacterial infection or a person has a compromised immune system.

Ischemic colitis

Treatment of ischemic colitis involves medical management. This may include measures such as:

  • IV fluid resuscitation, the administration of fluid through a vein
  • supplemental oxygen
  • allowing the bowel to rest by giving food that does not require digestion

If this does not work, a person may require surgery.

Below are some answers to common questions about FAC.

Is FAC dangerous?

This depends on what is causing the FAC. In some people, FAC does not cause any symptoms, but in other cases, it relates to serious medical conditions, such as ischemic colitis.

How is it different from ulcerative colitis (UC)?

UC is a distinct medical condition that can involve inflammation of a large portion of the colon. In contrast, FAC is inflammation in a small area, and it is not a medical condition in its own right but a symptom of something else.

A person with unexplained diarrhea, abdominal cramps, or other digestive symptoms should speak with a doctor. This does not necessarily indicate FAC, but it may suggest a person has a medical condition that requires treatment. In some cases, doctors may find evidence of FAC, but there are many causes for these symptoms.

A person should seek immediate medical attention if they have:

  • sudden, severe pain in the abdomen
  • bloody diarrhea
  • nausea

This could indicate ischemic colitis, which can require treatment.

Focal active colitis (FAC) is a microscopic finding in the colon. It occurs when white blood cells, known as neutrophils, enter crypts in the wall of the colon. It indicates the presence of inflammation in a small area.

FAC does not always occur with symptoms, but if it does, they may include diarrhea and weight loss. Various conditions can cause FAC, including Crohn’s disease, infectious colitis, IBS, ischemic colitis, and certain medications.

Doctors treat FAC by addressing the condition that is causing it.