CA 19-9

A tumour marker primarily used for pancreatic and biliary cancers.

What it is

CA 19-9 is a carbohydrate antigen elevated in pancreatic, biliary, and some gastrointestinal cancers. It is the most commonly used marker for pancreatic cancer monitoring, though it is not specific and can be elevated in benign conditions.

Why it matters

CA 19-9 is most valuable for monitoring treatment response in known pancreatic or biliary disease. A falling CA 19-9 with treatment is favourable. Approximately 10% of people are Lewis antigen-negative and cannot produce CA 19-9, making it uninformative in this group.

How to test

Blood test.

This information is for educational purposes only. Always discuss testing and interpretation of results with your care team.

Optimal range

Below 37 U/mL

normal

Above 37 U/mL

elevated — interpret with clinical context

How often

At baseline and each oncology review cycle if indicated.