Cancer Antigen 19-9

About the Test

Purpose of the test

The purpose of a CA 19-9 test is to measure the amount of CA 19-9 in the blood. CA 19-9 is a type of tumor marker. Tumor markers are substances found in tissue, blood, or other body fluids that may be a sign of cancer or certain noncancerous conditions. Testing may be performed for a number of reasons, including:

  • Diagnosing cancer and other medical conditions: CA 19-9 can be elevated as a result of pancreatic cancer and other cancers of the digestive system. It can also be increased by non-cancerous conditions such as scarring of the liver. Because it may be affected by multiple conditions, CA 19-9 testing is not used as the only test to make a diagnosis. Instead, CA 19-9 measurements are usually combined with the results of other tests, such as imaging and biopsy, to diagnose cancer or other diseases.
  • Evaluating cancer treatment: For people who have already been diagnosed with cancer, periodic monitoring of CA 19-9 can help doctors evaluate how the cancer is responding to treatment. In patients with pancreatic cancer, for example, a CA 19-9 level will generally be taken after diagnosis. This is referred to as a baseline measurement and can be compared to future levels taken during or after treatment.
  • Estimating cancer prognosis: The level of elevation of CA 19-9, both at initial diagnosis and after treatment, is one of several factors that may help doctors estimate a patient’s prognosis. Prognosis is the likely outcome of a disease, and it can also be affected by things like the stage or extent of a disease, any coexisting conditions, and a patient’s overall health.
  • Monitoring for cancer recurrence: Doctors may use CA 19-9 testing to evaluate pancreatic cancer patients who have received treatment with surgery to check for evidence of a recurrence. A recurrence is the return of a disease, usually after a period of time when it was not detectable.

CA 19-9 testing is not indicated for use as a method to screen for cancer. Screening refers to searching for evidence of a disease when there are no symptoms.

What does the test measure?

CA 19-9 testing measures the amount of cancer antigen 19-9 released into the bloodstream. This substance is produced by many cells in the body, including some types of healthy cells and certain cancer cells.

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