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Cancer Antigen 19.9 (CA 19-9) – Serum

Published: August 9, 2026Updated: August 17, 2026

This test measures the level of a protein (antigen) called CA 19-9 in your blood. It may help detect or monitor certain cancers, including pancreatic cancer, and sometimes other types of cancer that spread to the abdomen.

Quick summary

["CA 19-9 can help track how a cancer is growing or responding to treatment, but it’s not always the first test used for diagnosis."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
26924-1
Short code
CA19-9
Synonyms
Cancer Ag19-9 Fld-aCnc
Category
chemistry
Sample
serum
Container
Red-top serum tube (no anticoagulant) for serum collection; sterile container for body fluid collection
Units
N/A
Ref low
0
Ref high
37
Critical range
0.5 N/A – —
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
Immunoassay (e.g., chemiluminescent immunoassay or electrochemiluminescence immunoassay)
CPT
86301
SNOMED
395698004
Specimen volume
1-2 mL of serum or body fluid
Stability
Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 3 months (avoid repeated freeze-thaw cycles)
Hemolysis max
100
Lipemia max
150
Icterus max
25
TAT
4–24 hours
Order
routine

What Does CA 19-9 Measure?

CA 19-9 is a protein produced by some cancer cells, particularly pancreatic cancer. It can also be found in higher amounts in other cancers that affect the digestive system or spread to the abdomen. Your doctor may order this test if you have symptoms like abdominal pain, unexplained weight loss, or if you’ve been diagnosed with a cancer linked to this marker.

Why Might Your Doctor Order This Test?

A CA 19-9 test may be used to check for pancreatic cancer, especially if you have risk factors like a family history, smoking history, or symptoms. It can also help monitor pancreatic cancer after treatment to see if it’s coming back. In some cases, it may be used for other cancers, but it’s not a definitive test alone.

How Is the Test Done?

A blood sample is taken from a vein in your arm. The blood is sent to a lab where it’s analyzed to measure the CA 19-9 protein levels. The test usually takes a few days to get results, depending on lab processing times.

What Are Possible Results?

Higher-than-normal levels of CA 19-9 may suggest cancer, but it can also be elevated in other conditions like chronic pancreatitis, liver disease, or certain infections. A single high result doesn’t always mean cancer, so doctors often use it alongside other tests and imaging.

Reference range

Generally <37 U/mL is considered within normal limits; however, reference values may vary by laboratory and assay method. In body fluid, values should be interpreted in clinical context.N/A

Specimen: serum

No special preparation required. Fasting is not necessary. Inform clinician of any recent imaging studies involving contrast media.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

CA 19-9 is most commonly used to monitor pancreatic cancer progression or recurrence. While it’s not always accurate for early detection, it can be helpful in tracking treatment effectiveness. False positives or negatives can occur, so doctors rely on it alongside other diagnostic tools like imaging and biopsies. It’s also sometimes used for other cancers, but its role varies by situation.

Short name

CA 19-9 Blood Test

Frequently asked questions

Why might my CA 19-9 test be ordered?
Your doctor may order this test if you have symptoms of pancreatic cancer, a known risk for pancreatic cancer, or if you’ve already been diagnosed with a cancer linked to CA 19-9. It can also be used to check how well treatment is working or if cancer has returned.
What does a high CA 19-9 level mean?
A high level may indicate cancer, but it can also be caused by other health conditions like chronic pancreatitis or liver disease. Your doctor will consider your overall health and other test results before making a diagnosis or deciding on next steps.
Can CA 19-9 be used to diagnose cancer early?
No, CA 19-9 is not typically used for early cancer detection. It’s more commonly used to monitor existing cancer or check for signs of recurrence. Early diagnosis often relies on other tests, like imaging or biopsies, which can provide more detailed information.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy