What Is a CA 19-9 Number?
CA 19-9, also called cancer antigen 19-9 or carbohydrate antigen 19-9, is a type of protein found in your blood.
“We call CA 19-9 a tumor marker, which is a substance made by cancer cells or by normal cells in response to cancer,” says Gretel Terrero, MD, a gastrointestinal medical oncologist and associate director of community outreach at Sylvester Pancreatic Cancer Research Institute, part of the University of Miami Health System.
A CA 19-9 blood test is one of the tools doctors use in the diagnosis and treatment of pancreatic cancer. But this test cannot diagnose the disease on its own because your CA 19-9 level can also be higher due to other cancers or diseases.
How is CA 19-9 measured?
The CA 19-9 blood test, also called a CA 19-9 radioimmunoassay (RIA) test, is a simple blood test that can be done in your doctor’s office or clinic, similar to other routine lab tests. Results are usually available the same day or soon after.
What CA 19-9 Levels Mean
Your pancreas and bile duct systems produce the CA 19-9 protein, as do certain cells in the stomach, colon, uterus, and salivary glands. Normal values for CA 19-9 vary by the lab doing the test, but generally, levels of about 37 units per milliliter (U/mL) or higher are considered elevated.
“Patients can have elevated CA19-9 up to 50,000 U/mL or greater,” says Terrero. “Although at times, the amount of elevation correlates with volume of disease, it is not a perfect science, and there are certainly caveats to interpreting this tumor marker correctly.”
What if My Checkup Shows a Higher CA 19-9?
Doctors almost never depend on CA 19-9 test results alone to determine your diagnosis or decide on a treatment plan for pancreatic cancer, says Harsh Singh, MD, director of hepatobiliary and pancreas oncology at Mass General Brigham Cancer Institute in Boston.
“In isolation, it doesn’t necessarily become something that we would base anything on,” he says.
Scans are the gold standard for detecting the presence of cancer, Singh says.
“If scans look localized and the CA 19-9 levels are very high or higher than we would expect — not for another obvious reason — then we start wondering, ‘Is there more cancer than meets the eye, or evidence microscopically that there’s more cancer there?’” he says.
The CA 19-9 test can be useful, but it’s not a single tool that helps determine how to approach treatment.
An elevated CA 19-9 level in a healthy patient without concerning clinical symptoms “can lead to unnecessary anxiety and unnecessary imaging tests,” Terrero says. If you haven’t yet been diagnosed with pancreatic cancer, Terrero suggests discussing your clinical symptoms with your doctor and having the required lab tests and scans to further investigate the symptoms.
What Does My CA 19-9 Number Say About My Treatment?
Your doctor will track your CA 19-9 number “every few weeks while on various treatments to help understand whether the cancer is responding to the therapy,” Terrero says. “We expect for the tumor marker to decrease or ‘melt away’ as the cancer decreases in size — a desired response to treatment — and for it to increase as the cancer grows or is not responding to treatment. It is a very dynamic number, which is why it is important to follow it regularly in patients who are having cancer treatment.”
Typically, adds Singh, doctors watch trends over time when treating their patients.
The value of a given CA 19-9 number varies from patient to patient and is specific to your cancer and diagnosis, but a lower CA 19-9 number almost always indicates your treatment is working.
“For example, in pancreatic cancer, there are patients with diffuse metastatic disease (stage IV), yet their tumor marker is only in the 100 range, while other patients with localized cancer only in the pancreas (an earlier stage III) may have a tumor marker in the thousands range,” Terrero says. “Ultimately, what we want to see as we start their therapies is that each patient’s marker decreases as we continue to treat the cancer.”
Why Your CA 19-9 Number Doesn’t Tell the Whole Story
For about 80% of people with pancreatic cancer symptoms, the CA 19-9 test accurately predicts their diagnosis. However, about 5%-10% of the world’s population has a genetic difference that affects their bodies’ ability to make CA 19-9. They make low levels of CA 19-9 or none at all. These people can still have advanced pancreatic cancer, even though CA 19-9 is low or absent in their blood.
“CA 19-9 nonproduction is more prevalent in Black patients,” Terrero says.
Black people also have a higher incidence of pancreatic cancer than other racial and ethnic groups. Terrero says that research indicates worse outcomes in patients who do not produce CA 19-9.
Throughout your treatment journey, your doctor will usually check your CA 19-9 levels to get a sense of how effective the treatment is. Sometimes, your levels will rise right after the start of chemotherapy. This doesn’t always mean your cancer is not responding well; it may be a temporary surge of the tumor marker that will soon start to drop. Your CA 19-9 levels may also rise if you’re having radiation, as your cancer cells die and release the protein. Hence, your doctor may stop checking your CA 19-9 levels during radiation therapy.
Higher CA 19-9 levels can indicate the presence of other cancers in the colon/rectum, liver, stomach, and ovaries. But they can also signal noncancerous conditions, including:
- Bile duct inflammation, blockage, or infection
- Chronic hepatitis or kidney failure
- Liver disease
- Cystic fibrosis
- Pancreatitis
- Gallstones
- Lung disease
- Ovarian cysts
- Inflammatory conditions
- Thyroid conditions
Your CA 19-9 Number and Pancreatic Cancer Remission
How often you see your doctor after you go into remission depends on your treatment, the extent of your cancer, and other things. Usually, you’ll see your doctor every couple of months for several years after treatment, then less often if your cancer doesn’t come back. Your doctor will do scans and blood tests, including the CA 19-9 test, as part of your follow-up. It’s important to go to these visits, as well as follow through with any lab tests your doctor orders.
Takeaways
Because higher CA 19-9 levels can signal the presence of other types of cancer or noncancerous diseases, the CA 19-9 blood test is not used to screen for or diagnose pancreatic cancer. Rather, this tumor marker is used to examine your response to treatment, says gastrointestinal medical oncologist Gretel Terrero, MD. She says the test “should only be used in patients who already have a diagnosis of a certain type of cancer and their cancer specialist or oncologist is using this lab to follow the treatment response and help make treatment plan decisions.”
CA 19-9 Number FAQs
Which labs would be high with pancreatic cancer?
When used along with other diagnostic tests and an evaluation of symptoms, a CA 19-9 reading over about 37 U/mL might indicate that you have pancreatic cancer.
What cancers have elevated CA 19-9?
Other cancers, including bile duct, stomach, colorectal, liver, ovarian, bladder, lung, esophageal, and thyroid, can raise CA 19-9 levels.
What is the biggest indicator of pancreatic cancer?
Doctors examine your symptoms (such as fatigue, yellowing of the skin (jaundice) or the eyes, unexplained weight loss and poor appetite, back or belly pain, or an enlarged liver or gallbladder), perform imaging tests like CT scans or MRIs, and test for tumor markers such as CA 19-9 in your blood. Even with these diagnostic tools, the gold standard for a final diagnosis is a positive biopsy showing pancreatic cancer cells under the microscope.
