Cancer Antigen 19-9
Also known as:Carbohydrate Antigen 19-9; Cancer Antigen-GI; CA-GI; CA 19-9
Formal name:Cancer Antigen 19-9
Related tests:Bilirubin, Carcinoembryonic Antigen, Liver Panel, Tumor Markers
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Why Get Tested?
Primarily to monitor response to pancreatic cancer treatment and to watch for recurrence; sometimes to aid in the diagnosis of pancreatic cancer
When to Get Tested?
During and/or following pancreatic cancer treatment
A blood sample drawn from a vein in your arm; sometimes samples of other types of body fluids
Test Preparation Needed?
How is it used?
The CA 19-9 test may be used, along with other tests such as carcinoembryonic antigen (CEA), bilirubin, and/or a liver panel, to help evaluate and monitor a person who has been diagnosed with pancreatic cancer and is undergoing treatment.
CA 19-9 is used as a tumor marker:
- To monitor a person's response to pancreatic cancer treatment and/or cancer progression
- To watch for pancreatic cancer recurrence
- Sometimes to aid in the diagnosis of pancreatic cancer
CA 19-9 can only be used as a tumor marker if the cancer is producing elevated amounts of it. Since CA 19-9 is elevated in about 65% of those with bile duct cancer (cholangiocarcinoma), it may be ordered to help evaluate and monitor people with this type of cancer.
The CA 19-9 test is not sensitive or specific enough to use as a screening test for cancer. It is not currently useful for detection or diagnosis by itself because non-cancerous conditions can cause elevated CA 19-9 levels. Researchers continue to investigate markers to be used alone or in combination with CA 19-9 that may be more useful for screening for and detecting pancreatic cancer in the early stages, when it is most treatable.
When is it ordered?
CA 19-9 may be ordered when a person has been diagnosed with pancreatic cancer and/or has signs and symptoms that may indicate pancreatic cancer. Early signs and symptoms may be subtle and nonspecific. Examples include:
- Abdominal and/or back pain
- Loss of appetite
- Unexplained weight loss
In later stages, there may be chronic pain, nausea, vomiting, malabsorption, and, in some rare instances, problems with blood glucose control.
If CA 19-9 is initially elevated in pancreatic cancer, then a series of CA 19-9 tests may be ordered during cancer treatment to monitor response and on a regular basis following treatment to help detect recurrence.
CA 19-9 may sometimes be ordered when a healthcare practitioner suspects bile duct cancer in a person with a bile duct obstruction. Non-cancerous causes of bile duct obstruction can cause very high CA 19-9 levels, which fall when the blockage is cleared. In these cases, it is a good idea to wait at least a week or two after the blockage is relieved (by placing a tube, or stent, in the bile ducts) to re-check CA 19-9 levels.
What does the test result mean?
Low amounts of CA 19-9 can be detected in healthy people, and many conditions that affect the liver or pancreas can cause temporary elevations.
Moderate to high levels may be seen in people with pancreatic cancer, other cancers, and in several other diseases and conditions. The highest levels of CA 19-9 are seen in cancer of the exocrine pancreas. This cancer arises in the tissues that produce food-digesting enzymes and in the ducts that carry those enzymes into the small intestine. About 95% of pancreatic cancers are of this type.
Levels of CA 19-9 that are initially high and then fall over time may indicate that the treatment is working and/or that the cancer was removed successfully during surgery. Levels that remain high or rise over time may indicate that treatment is not working and/or that the cancer is recurring.
Is there anything else I should know?
Unfortunately, early pancreatic cancer gives few warning signs. By the time a person has symptoms and significantly elevated levels of CA 19-9, pancreatic cancer is usually at an advanced stage.
CA 19-9 is a protein on the surface of cells. It is derived from a blood group antigen called Lewis antigen that is similar to the ABO antigens that are used in blood typing for transfusions. About 5% to 7% of people are Lewis antigen negative (about 30% in people of African ancestry) and do not produce CA 19-9. The CA 19-9 test is not useful for monitoring people who are Lewis antigen negative.
Laboratories may use different methods to test for CA 19-9, so results can vary from lab to lab. If you are having a series of CA 19-9 tests done, it is advised that you have the tests done by the same method, typically by the same laboratory, so that the results can be compared and interpreted correctly. You may wish to discuss this issue with your healthcare practitioner.
What is being tested?
Cancer antigen 19-9 (CA 19-9) is a protein that exists on the surface of certain cancer cells. CA 19-9 does not cause cancer; rather, it is shed by the tumor cells and can be detected by laboratory tests in blood and sometimes other body fluids. This test measures the level of CA19-9.
Since CA 19-9 can be measured in blood, it is useful as a tumor marker to follow the course of the cancer. CA 19-9 is elevated in about 70% to 95% of people with advanced pancreatic cancer. (Read more on the Test tab of this article and in the Pancreatic Cancer article.)
However, CA 19-9 may also be elevated in other cancers, conditions, and diseases such as: gallbladder and bile duct cancers (cholangiocarcinoma), colorectal cancer, gastric cancers, ovarian cancer, lung cancer, liver cancer, bile duct obstruction (e.g., gallstones), pancreatitis, cystic fibrosis, thyroid disease, and liver disease. Small amounts of CA 19-9 are present in the blood of healthy people. Since CA 19-9 is not specific for pancreatic cancer, it cannot be used by itself for screening or diagnosis.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. Sometimes, a healthcare practitioner will collect samples of other body fluids.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
- Why is my healthcare practitioner not screening me for CA 19-9?
CA 19-9 is not sensitive or specific enough to be recommended as a screen for people who do not have symptoms. There are too many false positives and false negatives associated with it. Researchers are looking for other markers that may help detect pancreatic cancer at an earlier stage and that may be more suitable for screening.
- What other procedures will my healthcare practitioner likely order along with CA 19-9?
Your healthcare practitioner may order a CT scan (computed tomography), an ultrasound, an MRI scan to look at the pancreatic and bile ducts, an ERCP (endoscopic retrograde cholangiopancreatography, a procedure in which a small lighted tube is passed through the mouth and stomach into the duodenum and then into the bile and pancreatic ducts), and/or a biopsy to look for cancer cells under the microscope.
- What are the main risk factors for pancreatic cancer?
Healthcare practitioners still do not know what causes most cases of pancreatic cancer. Identified risk factors include tobacco use (smoking and smokeless products), age (most are over 50 years old), sex (men are slightly more likely to have it than women), family history, diabetes, chronic pancreatitis, and workplace exposure to certain chemicals, such those used in the dry cleaning and metal working businesses.
© 2017 American Association for Clinical Chemistry, republished from Lab Tests Online.*
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