CA 19-9 is a protein that is released by some types of tumor cells and is therefore used as a tumor-marker to aid in the diagnosis of some cancers, such as pancreatic, liver, gallbladder or colorectal cancer. These cancers are associated with high CA 19-9 levels.

However, high CA 19-9 levels can also be a sign of other diseases that not related to cancer, such as pancreatitis, gallbladder stones, liver cirrhosis or cystic fibrosis, for example.

The CA 19-9 test is simple and is done by collecting a blood sample that is analyzed in the laboratory. Results should be interpreted by the ordering physician.

Normal CA 19-9 levels

CA 19-9 levels are considered to be normal if they are under 37 U/mL. High CA 19-9 levels are typically above 37 U/mL, and may be a sign of cancer, typically pancreatic cancer.

High CA 19-9 levels can also be above 37 U/mL with health conditions like pancreatitis, bile duct obstruction or liver cirrhosis.

What is it for

The CA 19-9 exam is indicated to assist in the diagnosis of:

Pancreatic cancer
Colorectal cancer
Gallbladder cancer
Liver cancer

Furthermore, in addition to assisting in diagnosis, the CA 19-9 test allows the doctor to evaluate the response to cancer treatment, since CA 19-9 levels tend to increase with tumor growth and reduce as the tumor shrinks.

CA 19-9 testing may also be ordered in the cases of suspected pancreatitis, cystic fibrosis, gallstones, cholecystitis, or liver cirrhosis.

A CA 19-9 test can be ordered when certain symptoms of gastrointestinal cancer appear, like frequent nausea, swollen belly, weight loss, yellowish skin or abdominal pain, as a high or low result can prompt further testing or rule out this condition.

Other tests the doctor can order alongside a CA 19-9 test include a CEA test, bilirubin and liver function tests.

How the test is done

The CA 19-9 exam is performed like a normal blood test, in which a blood sample is collected and sent to the laboratory for analysis. No specific preparation is required for this type of clinical analysis.

Interpreting results

The results of the CA 19-9 exam should be interpreted by the ordering doctor, along with other requested tests.

After the first CA 19-9 test, the test can be repeated several times to check the effectiveness of cancer treatment. Possible results include:

Increasing CA 19-9 levels: it means that the treatment is not having a therapeutic result and that the tumor is increasing, leading to greater production of CA 19-9 in the blood;
Stable CA 19-9 levels: it may indicate that the tumor is not growing or shrinking, which may prompt the doctor to change the treatment approach
Decreasing CA 19-9 is levels: this is generally a sign that the treatment is effective and therefore the cancer is reducing in size;
Low CA 19-9 after treatment, but then increased again: this may indicate that the cancer has returned or grown.

In some cases, the result may increase over time even if the cancer is not actually increasing in size, but this is usually more common patients who undergo radiation therapy.