CA 19-9 (Cancer Antigen 19-9) – Serum Test

Overview:
CA 19-9 is a carbohydrate antigen used as a tumor marker mainly for pancreatic cancer. It is a glycoprotein expressed on the surface of some cancer cells and released into the bloodstream. Elevated serum levels of CA 19-9 are associated with pancreatic cancer but can also be raised in other gastrointestinal cancers and some benign conditions.

Sample Type:
Serum (blood sample from which cells have been removed).

Purpose:

To monitor treatment response and disease progression in pancreatic cancer patients.

To detect recurrence or metastasis of pancreatic or other gastrointestinal cancers.

Sometimes used in conjunction with other diagnostic tools but not recommended as a sole screening test.

How It Works:
The CA 19-9 level is measured by immunoassays that detect the antigen concentration in the serum. Normal values are typically less than 37 U/mL, but reference ranges may vary slightly by laboratory.

Clinical Significance:

High levels of CA 19-9 can indicate pancreatic adenocarcinoma or other malignancies such as colorectal, gastric, liver, and bile duct cancers.

Elevated CA 19-9 may also occur in benign conditions like pancreatitis, liver cirrhosis, cholangitis, and cystic fibrosis.

Useful for tracking disease course rather than initial diagnosis.

Limitations:

Not specific enough for screening or diagnosis alone due to elevations in benign diseases.

Some individuals (approximately 5-10%) are genetically unable to produce CA 19-9, resulting in false-negative results.