Lab tests for colorectal cancer

This page was reviewed under our medical and editorial policy by

Maurie Markman, MD, President, Medicine & Science

This page was updated on March 16, 2022.

Screening for colorectal cancer may help prevent the disease or catch it at an early stage, when it’s most treatable. Colonoscopy is the gold standard for finding colon polyps that could become cancer, but it’s not the only option. Stool tests provide another tool for screening. Several stool tests may be used to determine whether the stool has blood or genetic markers, which may be a sign of cancer or precancerous polyps.

Each test has its advantages and disadvantages. Speak with your health care provider about which may be appropriate for you and why.

Below are some stool and other tests your doctor may order during diagnosis and colorectal cancer treatment.

Stool tests for colorectal cancer

These tests include:

Stool DNA test: This test requires a prescription and is sold under the brand name Cologuard®. It is approved by the U.S. Food and Drug Administration to detect mutated DNA in the stool. The stool sample is collected at home and mailed to a laboratory. The test does not require special preparation or medication restrictions. A stool DNA test may be an acceptable alternative to a colonoscopy for some low-risk patients, but is not recommended for patients who have had polyps, a family history of colorectal cancer or other risk factors.

Fecal immunochemical test (FIT): This analysis uses antibodies to detect blood in the stool. This test may also be performed at home. Test kits include a brush or stick used to wipe the stool sample onto a test card. Some test kits offer results in minutes; others are mailed to a lab. The FIT test does not require special preparation or medication restrictions.

Fecal occult blood test (FOBT): This test uses the chemical guaiac to detect blood in the stool. Like the FIT test, a sample is wiped onto a test card. Results may be provided immediately or after the samples are sent to a lab. This test may also be performed at home and may require some dietary and medication restrictions.

All test results should be discussed with a doctor to determine the next steps in the diagnostic or staging process or to discuss whether treatment is required.

Stool tests may be recommended every three years. A follow-up colonoscopy may be needed if the test results are positive.

Blood tests for colorectal cancer

No blood tests are recommended to be used for colorectal cancer screening at this time. However, your doctor may check your blood for tumor markers or biomarkers, proteins made in response to cancer. Tumor markers also may refer to mutations or changes in your cells that are indicative of certain cancers. To screen for average-risk adults aged 50 and older, the U.S. Food and Drug Administration has also approved a blood-based biopsy, also called a liquid biopsy, that tests for a mutation in the SEPT9 gene.

Other lab tests for colorectal cancer

In addition to stool tests, other lab tests may be recommended to help doctors diagnose and stage colorectal cancer and/or follow the progress of your treatment.

These include:

Genomic tumor assessment: Genomic testing is used to analyze a tumor on a molecular level to identify DNA alterations that may be driving the cancer’s growth. By identifying the mutations in a cancer cell's genome, doctors may better understand what caused the tumor and tailor treatment based on these findings. Learn more about genomic tumor assessment.

CBC test: Complete blood count (CBC) tests may be used to measure different types of cells in the blood. A CBC blood test may be particularly helpful in determining whether you have too few red blood cells, which causes anemia. This may be a concern for colorectal cancer patients, because it may indicate that they have a tumor that’s been bleeding for some time.

Liver function tests: These blood tests may be performed to assess the function of the liver and determine whether colorectal cancer has spread to that organ.

Tumor marker tests: This blood test may be used in addition to other tests for patients who are being treated for colorectal cancer. Tumor marker tests are used to check for two substances in the blood that colorectal cancer may produce: carcinoembryonic antigen (CEA) and CA 19-9. The tests may help determine an appropriate course of treatment and, sometimes, whether the disease is likely to recur.

Nutrition panel: This test may be used to evaluate patients for nutrient deficiency, such as low vitamin D and iron. The test helps identify the nutrients patients may need replaced or boosted to support their quality of life.

Next topic: How is colorectal cancer treated?

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