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CA19-9

Blood Sciences Test


Specimen

Serum

Special Instructions

Only available to Directorate of Medicine

Units

U/mL

Reference Range

0- 34 U/mL

Test Usage

CA 19.9 is a tumor-associated antigen, originally isolated from a human colon cancer cell line. It is present on gangliosides in tissues, but is carried by glycoproteins in serum. The oligosaccharide, bearing the CA 19.9 antigen, is related to sialylated Lewis A blood group antigen. Lewis A antigen must be present before CA 19.9 can be expressed. CA 19.9 is synthesized by normal cells in pancreatic and bile ducts, gastric and colonic mucosa, bronchial and salivary glands, endometrium, and prostate. Secretions from these organs are rich in CA 19.9, but very little antigen appears in the blood of healthy individuals.

Even though CA 19.9 was originally isolated from a colon cancer cell line, its greatest clinical utility is detecting pancreatic cancer. CA 19.9 is not a very useful screening test for pancreatic cancer in asymptomatic patients. The maximum achievable sensitivity is 95%, since 5% of the UK. population are Lewis a & b nonsecretors and do not synthesize CA 19.9. In practice, the sensitivity for early cancer is much less. Serum levels are elevated in less than 30% of patients with stage 1 cancers.

Elevated CA 19.9 levels are not specific for pancreatic cancer, but are elevated in other benign and malignant disorders. Other GI malignancies are also associated with elevated CA 19.9 levels, but not usually to the same extent as pancreatic cancer. CA 19.9 is elevated in 67% of bile duct cancers, 41% of gastric cancers, 34% of colon cancers, 22% of esophageal cancers, 49% of hepatomas, and 14% of non-gastrointestinal tract cancers. Most benign disorders cause lower elevations of serum CA 19.9. However, two benign conditions, cirrhosis and acute cholangitis, can cause high CA 19.9 levels. In acute cholangitis, levels rapidly return to normal following decompression of the common duct.

CA 19.9 is the most useful circulating tumor marker for evaluating patients who present with signs and symptoms of a chronic pancreatic disorder. In this population the prevalence of cancer is about 17%. Using an upper limit of normal of 40 U/mL, serum CA 19.9 assays have a sensitivity of 81%, specificity of 90%, and a positive predictive value of 72%. The specificity and positive predictive value for cancer increase with higher CA 19.9 values. The higher the CA 19.9 level, the greater the likelihood of cancer. Levels >300 have a positive predictive value of 92%.

Turnaround time

7 days

Availability

Local test

Can be added on to an existing request up to 4 days following sample receipt

Minimum Repeat Interval

18 days

Specimen Labelling Procedure
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A UKAS Accredited Medical Laboratory

8210

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