Tumor markers
CA 19-9
Sialyl-Lewis A antigen; pancreaticobiliary cancer marker.
Sample
Serum
Clinical reference range
— to 37 U/mL
Adult
Conv: —–37 U/mL
Biology
What it measures
Carbohydrate antigen on a Lewis blood-group glycolipid. ~5–10% of patients are Lewis-negative and cannot produce it.
Clinical use
Why we order it
Pancreatic adenocarcinoma surveillance and prognosis.
Differential
Causes of abnormal values
Causes of HIGH
- ↑Pancreatic cancer
- ↑Cholangiocarcinoma
- ↑Cholestasis (any cause)
- ↑Pancreatitis
- ↑Cirrhosis
Pitfalls
Pre-analytic & interpretation traps
- !Cholestasis alone (e.g., obstructed CBD stone) can elevate CA 19-9 into the thousands — recheck after biliary decompression.