Fecal Immunochemical Test

The fecal immunochemical test (FIT) looks for hidden blood in the stool. This test is most commonly used to screen for colorectal cancer, but it can find gastrointestinal bleeding caused by other conditions. FIT uses a stool sample collected at home.

While the FIT generally produces more reliable results than other stool-based tests, it cannot diagnose any condition. If abnormal results are found, more specialized testing may be needed.

Purpose of the test

The primary purpose of the FIT is to help find colorectal cancer or precancerous polyps early. A colon polyp is a small mass of cells. Most polyps do not cause harm, but some can become cancerous if they are not removed.

Both colorectal cancers and polyps release trace amounts of blood that is excreted with stool. A microscopic amount of blood in the stool can be one of the first signs of colorectal cancer. Diagnosing colorectal cancer early can make it easier to treat.

The FIT is used as a screening test, meaning that it checks for signs of cancer or polyps in people who do not otherwise have symptoms of these conditions. The FIT is not used in people who are already known to have colorectal cancer.

Blood in the stool can have causes other than polyps and cancer, such as hemorrhoids and ulcers. The FIT cannot determine the specific source of the blood or what is causing it, only whether blood is present. More specialized or invasive testing may be necessary if blood is found or if other symptoms are present.

What does the test measure?

The FIT measures hemoglobin, a protein in red blood cells.

To check for hemoglobin, the stool sample is combined with a liquid. The sample is then placed in a machine or device with antibodies, a type of protein, that specifically bind to hemoglobin. The machine then indicates whether hemoglobin is present.

The FIT only detects intact hemoglobin. This means that it does not detect partially digested hemoglobin originating in the upper gastrointestinal system. Additionally, because the FIT measures human hemoglobin, the test is unaffected by hemoglobin found in some foods.

How to get tested

A FIT can be ordered by your doctor. FIT test kits can also be purchased over-the-counter without a prescription at a pharmacy, through online retailers, or directly from the test manufacturer.

The FIT requires you to collect a stool sample, which is usually done at home. Depending on the brand of FIT kit, the sample is then returned to the doctor’s office or mailed directly to the laboratory for analysis. Some brands of FIT allow you to analyze the sample at home.

Can I take the test at home?

FIT stool samples are usually collected at home. FIT kits are often provided by a doctor or laboratory technician, but they can also be purchased over-the-counter.

FIT kits are available for direct purchase by consumers. There are currently over 30 different over-the-counter FIT kits  that have been cleared or approved by the Food and Drug Administration for use. Many at-home FIT kits require that you mail your sample to a laboratory for analysis, while others provide results at home within minutes.

If you receive a positive result using an over-the-counter FIT kit, it will be important to discuss the next steps for your care with a doctor.

How much does the test cost?

The cost of an FIT depends on whether you have medical insurance and what your insurance covers. Your insurance may cover the full cost of an FIT, or you may be responsible for some out-of-pocket costs, such as copays and deductibles. It’s always a good idea to check with your doctor and insurance plan to clarify what costs you will need to cover, if any.

The price of over-the-counter FIT kits can range considerably, costing anywhere from $10 to over $100. You can ask your insurance provider whether they offer reimbursement for the cost of an over-the-counter FIT kit. Some insurance plans may require that a health professional order the kit in order to cover the test.

The FIT requires you to collect a stool sample using a small brush or stick and collection cup. The sample can be collected at home. Depending on the brand of FIT, you will then either analyze the sample at home or mail the sample to the doctor or a laboratory for analysis.

Before the test

The FIT is a straightforward test with no significant preparation needed. It does not require sedation or recovery time.

Because the FIT does not detect dietary hemoglobin, no special diet is required prior to the test. Medications will not alter test results, and in most cases, it is unnecessary to restrict their use, unless your doctor instructs you to.

During the test

A FIT kit will come with step-by-step instructions. Different brands can vary in the specific method for collecting a sample, but most follow a similar procedure for specimen collection:

1. Flush the toilet prior to use.
2. After a bowel movement on top of a collection container, place your used toilet paper into the kit waste bag.
3. Use the stick or brush from the kit to collect a stool sample as instructed.
4. Insert sample stick or brush to the sampling bottle
5. Mail the sampling bottle the same day you collect it as instructed.

This is a fairly quick process, typically completed in minutes. While some individuals may feel squeamish collecting the sample, there is no pain or risk involved.

After the test

There is no downtime needed after the test. You can resume normal activities immediately.

Most FIT kits require you to send the sample to your doctor or to a laboratory for analysis. It is important to mail the sample to the laboratory or doctor within one day of collection. Waiting several days can compromise the effectiveness of the test.

If you are using a FIT kit that provides results at home, carefully follow the FIT kit instructions for analyzing the sample yourself.

Receiving test results

Depending on the brand of FIT and where it was obtained, test results may be given in several ways.

Tests that analyze the sample in a laboratory typically make results available within one to five days. The laboratory may send results directly to your doctor to review with you. You may also be able to view results through your electronic medical chart.

If the FIT is completed through an over-the-counter test kit and mailed to the company laboratory, results are typically provided through the company’s website or smartphone application.

Over-the-counter FIT kits that advertise rapid results typically give results within five minutes. The results display in a small window of the test kit.

Interpreting test results

Most FITs report results as being either positive, negative, or invalid rather than a numerical value.

A positive test result, also called an abnormal result, means that the sample contains blood. It does not necessarily mean you have colorectal cancer, since noncancerous conditions can also cause blood to enter the stool. If you have a positive result, it is important to speak with your doctor about your test result. Your doctor may recommend a colonoscopy or other exam to assess the health of the colon and rectum.

A negative test result means that no blood was detected. This is considered normal. However, a negative result does not rule out colorectal cancer or polyps since not all cancers and polyps bleed.

An invalid result means that the test did not work properly. You may need to perform a new test. Be sure to review all packaged instructions carefully.

If you are using an over-the-counter rapid FIT kit, make sure that you are carefully reading the manufacturer’s instructions for interpreting results. In these kits, a positive, negative, or invalid result is typically indicated by the presence or absence of lines on the display of the test device.

How is a FIT different from a guaiac fecal occult blood test (gFOBT)?

Both the FIT and gFOBT test for hemoglobin in the stool to screen for colorectal cancer. However, the gFOBT uses a different chemical method to detect hemoglobin, which makes the test different in some key ways. Unlike the FIT, the gFOBT is affected by hemoglobin in the foods you eat and certain medications. It’s therefore important to restrict certain foods and medicines for several days before the test. Additionally, multiple samples must be collected for the gFOBT.

How is a FIT different from a FIT-DNA test?

A FIT-DNA test looks for changes in the DNA found in colorectal cells naturally excreted in stool in addition to hemoglobin. The FIT-DNA requires you to send an entire bowel movement to a laboratory.