CA 19-9 (Cancer Antigen 19-9)
A sugar-and-protein molecule that some digestive-system cancers release. Many harmless bile duct, liver and pancreas conditions raise it too.
AI-verified against cited sources. Awaiting expert reviewAlso called CA 19-9, CA19-9LOINC 24108-3
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What it is
CA 19-9 is a carbohydrate antigen, which is a sugar attached to a protein or fat. It is found on cells in the pancreas, bile ducts and gut. Small amounts are normally in the blood. Making CA 19-9 needs an enzyme that belongs to the Lewis blood group system, so a small share of people can't make it at all. That means a low result is not always reassuring.
Why it matters
Doctors mostly use CA 19-9 to follow people who have already been diagnosed with pancreatic cancer or some bile duct cancers, to see if treatment is working or if the cancer has come back. It isn't a good test for finding cancer in people with no symptoms. Many harmless conditions raise it, and some people with cancer have a normal value. A CA 19-9 result can't diagnose anything on its own.
If it’s high
A result above your lab's range does not mean you have cancer. The most common reasons are a blocked or inflamed bile duct, gallstones, pancreatitis and liver disease. Higher values are more common in people with pancreatic and some other digestive cancers. Your clinician will look at the number together with your symptoms, liver tests, imaging and other results, and may repeat it.
Common causes
- Gallstones or other blockage of the bile ducts
- Infection of the bile ducts (cholangitis)
- Inflammation of the pancreas (pancreatitis)
- Cirrhosis or other liver disease
- Cystic fibrosis
- Cancers of the pancreas, bile ducts, gallbladder, stomach or colon, and ovarian or bladder cancer
What can help
- Ask your clinician whether liver tests or imaging could show a blocked or inflamed bile duct
- Tell your clinician about liver or gallbladder problems, pancreatitis, and any biotin supplements you take
- Ask whether to repeat the test before drawing conclusions
- Use the same lab and method for follow-up tests
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 0–35 U/mL. Source: Labcorp, Mayo Clinic Laboratories.
- Adults (this one applies)0–35 U/mL
Sources: Labcorp, Mayo Clinic Laboratories
What can affect your result
- Lewis blood group: roughly 3 to 10 in 100 people can't make CA 19-9, depending on the source, so their result is not informative
- Blocked bile ducts, even a mild one, can raise CA 19-9 clearly
- Pancreatitis and liver disease
- Assay method: results from different methods can't be compared directly
- Biotin supplements and antibodies to animal proteins can interfere with some methods
- High-dose biotin (vitamin B7, found in many hair, skin and nail supplements) can interfere with some immunoassays. Mayo asks people to avoid biotin for 12 hours before the draw. Labcorp notes the same risk for its method and asks for 72 hours.
- Antibodies to animal proteins, for example after some scans or treatments that use animal antibodies, can disturb the assay (Mayo).
- Blocked or inflamed bile ducts, pancreatitis and liver disease can raise CA 19-9 without cancer.
- People who are Lewis-negative can't make CA 19-9, so their result can be low or undetectable even if a cancer is present.
- Results from different methods can't be compared directly, so use the same lab and method when following results over time.
When to talk to a clinician
Talk with your clinician soon if your CA 19-9 is above your lab's range, particularly if it keeps rising on repeat tests. Get care promptly for yellowing of your skin or eyes, belly pain, unexplained weight loss or unusual weakness. Get urgent care for fever and chills together with belly pain or yellowing of the skin.
Questions you could ask
- Why was CA 19-9 ordered for me, and how will we use the result?
- If I'm being followed for a cancer, how often should it be checked, and should I use the same lab each time?
- Could a blocked bile duct, gallstones, pancreatitis or liver disease explain this number?
- Should we repeat it, and should we check my liver tests or get imaging?
- Could I be unable to make CA 19-9, and does that matter for how we read my results?
Questions people ask
My CA 19-9 is in range. Does that rule out pancreatic cancer?
No. Some people with cancer have a normal CA 19-9. About 3 to 10 in 100 people can't make it at all, so their result doesn't tell us anything. CA 19-9 is not used to find cancer in people with no symptoms. If you have symptoms or a concern, talk with your clinician.
Can a harmless condition raise CA 19-9?
Yes. Gallstones, a blocked or infected bile duct, pancreatitis, liver disease and cystic fibrosis can all raise it. Mayo notes that in benign conditions such as cirrhosis, cholestasis and pancreatitis, values are usually below 1,000 U/mL. Your clinician can sort out which cause fits.
Why does my report show a different range than 35?
Labs use different methods. Labcorp prints 0 to 35 U/mL and Mayo Clinic Laboratories prints under 35. Some labs use 37. Values from different methods can't be compared directly, so use the range on your own report.
Show the science and sources
Units
- 1 U/mL = 1 U/mL
- 1 U/mL = 1 kU/L
Is a change real?
CA 19-9 naturally varies about 4.3% from test to test in the same healthy person. Between two results from the same lab, a rise of 14% or more, or a fall of 12% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Critical review and meta-analysis of biological variation estimates for tumor markers (Marques-Garcia F et al., EFLM WG-BV).
For clinicians and researchers
CA 19-9 is a sialylated Lewis-a blood group antigen carried on a mucin or glycolipid of roughly 10 kDa and measured with monoclonal antibody 1116-NS-19-9 (Labcorp). Mayo describes it as a modified Lewis(a) antigen that needs a fucosyltransferase to be made. People who are Lewis a-negative and b-negative can't express it: Labcorp cites 3% to 7%, Mayo 5% to 7%, and a 2012 evidence review 5% to 10%. Even Lewis-positive people can make varying amounts because of gene dosage (Labcorp). The mucin is cleared through the liver, so even slight cholestasis can raise serum CA 19-9 (Labcorp), and the 2012 review reports false positives in 10% to 60% of people with obstructive jaundice. Mayo notes benign elevations are usually below 1,000 U/mL. In symptomatic patients the review gives a sensitivity of 79% to 81% and a specificity of 82% to 90% for pancreatic cancer, and a positive predictive value of only 0.5% to 0.9% when used for screening, so it is not a screening test (Mayo, Labcorp and the review agree). Mayo says serial monitoring should start before treatment to set a baseline, and that single values are less informative. Methods: Labcorp uses an electrochemiluminescence immunoassay (ECLIA); Mayo uses the Beckman Access GI Monitor immunoassay. Both warn that values from different methods can't be compared directly. Reference limits: Labcorp 0 to 35 U/mL, Mayo under 35 U/mL; some studies and labs use 37 U/mL. Interference: biotin, and anti-animal antibodies (Mayo). Many labs and some reports state units as U/mL or kU/L; the two are numerically identical.
LOINC 24108-3 (primary), 83084-4. Specimen: serum.
Sources
- Carbohydrate Antigen (CA) 19-9 (test 002261), Labcorp
- CA19 - Overview: Carbohydrate Antigen 19-9 (CA 19-9), Serum, Mayo Clinic Laboratories
- CA 19-9 Blood Test (Pancreatic Cancer), MedlinePlus (National Library of Medicine) (2026)
- The clinical utility of serum CA 19-9 in the diagnosis, prognosis and management of pancreatic adenocarcinoma: An evidence based appraisal, Journal of Gastrointestinal Oncology (2012)
- Tumor Marker Tests in Common Use, National Cancer Institute (2023)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.