Serum or plasma concentration of cytokeratin 20 (CK20)

Your doctor may order this test to help identify the type of tumor found in a tissue sample, since CK20 is a protein made by certain cancer cells. It is often used to tell colorectal, gastric, or Merkel cell cancers apart from other tumor types, to check whether cancer has spread, or to learn more about a growth discovered during an earlier biopsy.

Your healthcare provider may recommend this test if you have symptoms like unexplained weight loss, abdominal pain, or unexplained bleeding. It could also be used to check for conditions like inflammatory bowel disease, pancreatic cancer, or gastrointestinal cancers such as colorectal cancer. Doctors may also order it to monitor treatment progress or recurrence in certain cancers.

Little preparation is usually needed because this test is most often performed on a tissue sample that was already collected during a biopsy or surgery. Tell your healthcare provider about all medicines you take, especially blood thinners, and mention any allergies or bleeding problems. If a new sample must be collected, your care team will give you specific instructions to follow beforehand.

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the blood draw if your test involves serum. Avoid smoking or consuming alcohol for a few hours beforehand. If you’re on blood thinners, let your provider know.

The test is carried out in a laboratory on a small piece of tissue, usually taken during a biopsy or a surgical procedure. A pathologist treats the sample with special stains that make CK20 protein visible under a microscope. If a blood sample is needed instead, a technician will simply draw blood from a vein in your arm, which is a quick and routine procedure.

A healthcare professional will draw blood from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause significant discomfort. The blood sample is then sent to a lab for analysis.

The results show whether CK20 protein is present in the tested tissue. A positive result suggests the tumor began in certain epithelial cells, often in the digestive tract or the skin, while a negative result points toward other origins. Your doctor will read the finding together with other markers, imaging, and your medical history, because no single result tells the whole story on its own.

Results are reported as a concentration (e.g., micrograms per liter). Higher levels may suggest conditions like gastrointestinal cancers, inflammatory bowel disease, or certain infections. Lower levels may indicate normalcy or other underlying issues. Your provider will interpret results in the context of your symptoms and medical history.