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What is the CA 19-9 Radioimmunoassay (RIA) test?  What does the CA 19-9 test measure?
The CA 19-9 Radioimmunoassay (RIA) is a simple blood test that measures the level of tumor-associated antigens found in the blood.  Antigens are substances that cause the immune system to make a specific immune response.  CA 19-9 antigens are foreign substances released by pancreatic tumor cells.

The normal range of CA 19-9 in the blood of a healthy individual is 0-37 U/ml (Units per milliliter).  CA 19-9 associated antigen levels are elevated in many patients with pancreatic cancer.  It is important to note that not every patient with pancreatic cancer will have an elevated CA 19-9 level. In addition, some non-cancerous conditions can cause high CA 19-9 levels.  For these reasons, the CA 19-9 test cannot be used as a diagnostic or screening test for pancreatic cancer. 

When is the CA 19-9 test performed?
After the diagnosis of pancreatic cancer is confirmed and if the CA 19-9 level was elevated before treatment, the CA 19-9 test may be used to judge the effectiveness of treatment.

What do the values or numbers of a CA 19-9 test mean?
In general, gradually rising CA 19-9 values indicate that the tumor is growing. If the values remain the same, then the disease may be stable.Decreasing CA 19-9 values may indicate that treatment is working and that the tumor or amount of cancer in the body is decreasing. A decline in CA 19-9 levels after treatment for pancreatic cancer followed by a rise later may suggest tumor recurrence or progression.

Why is the CA 19-9 test performed?
Changes in CA 19-9 levels help determine if the tumor is growing, remaining stable or getting smaller.  This test helps doctors decide if treatment should be changed or if additional tests or scans are necessary.

How is the CA 19-9 test performed?
A blood sample is taken from the patient and then sent to a laboratory for testing to determine the level of CA 19-9 present in the blood.  This blood sample is measured using a radioimmunoassay, or RIA, test.  Radioimmunoassay is a laboratory technique that can identify specific substances in the blood.

How often is the CA 19-9 test performed?
The doctor will determine how frequently the CA 19-9 tests should be performed.  If the tumor seems to be growing despite treatment efforts, the CA 19-9 test may be repeated weekly or after each round of treatment is completed.  In a patient who is not currently receiving treatment, the CA 19-9 test may be used periodically over time to determine if that patient should resume treatment or undergo additional testing.  People who had their tumors surgically removed might have periodic CA 19-9 tests as part of their follow-up care.

Can conditions other than pancreatic cancer cause an elevated CA 19-9?
Yes.  While a high CA 19-9 is most commonly associated with pancreatic cancer, other cancers, such as colorectal, lung, and gallbladder cancers, can also cause elevated levels.  High CA 19-9 levels can also be caused by non-cancerous conditions such as gallstones, a blockage of the bile duct (jaundice), pancreatitis, cystic fibrosis, and liver disease.

During radiation therapy, CA 19-9 levels might be elevated due to the dying cancer cells releasing CA 19-9.  Since the results of a CA 19-9 test are not accurate, the test is not performed while the patient receives radiation treatment.

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