Carbohydrate Antigen 19-9 (CA 19-9)
Other marker
CA 19-9
Carbohydrate Antigen 19-9 (CA 19-9)
A carbohydrate tumour-associated antigen used chiefly as a marker for pancreatic and biliary tract cancers, and sometimes to monitor other gastrointestinal malignancies. It is most useful for monitoring a known cancer rather than screening healthy people.
PED Notes
Appears on comprehensive panels but has little PED-specific relevance. The key interpretive caveats: individuals who are Lewis-antigen negative (roughly 5-10% of people) cannot produce CA 19-9 at all, so a normal value never excludes disease in them, and benign obstructive or inflammatory conditions of the bile ducts, pancreas, or liver can raise it substantially. Treat a mild isolated elevation in a healthy athlete as far more likely benign than sinister.
When high
When elevated (>37 U/mL):
- Benign causes are common and can produce striking elevations: biliary obstruction, cholangitis, pancreatitis, cirrhosis, and other liver disease. Correct any cholestasis and recheck, as CA 19-9 often falls once obstruction resolves
- The marker is most meaningful for tracking a diagnosed pancreatic or biliary cancer; it is not recommended as a screening test in asymptomatic individuals
- A markedly elevated or rising value without a benign explanation warrants imaging (cross-sectional abdominal imaging) and specialist review
- Remember the Lewis-negative caveat when a value is unexpectedly normal in a symptomatic person
Action: Do not self-diagnose from a single mildly raised CA 19-9. Address any liver/biliary inflammation, repeat the test, and escalate to a gastroenterologist only for persistent or rising elevations.
History Chart
Reading History
Frequently Asked Questions
Reference Ranges
Standard Range