CA 19-9 test
The CA 19-9 test is a blood test that measures the level of a specific glycoprotein known as carbohydrate antigen 19-9, which is primarily associated with certain types of cancers, particularly gastrointestinal tract carcinomas such as pancreatic, stomach, colon, and ovarian cancers. This protein can also be found in various normal tissues and bodily fluids, including the pancreas, saliva, and meconium. While the CA 19-9 test is not suitable for cancer screening due to its lack of sensitivity and specificity, it serves as a valuable tumor marker for monitoring the effectiveness of treatment and detecting recurrences in pancreatic cancer patients.
Typically, CA 19-9 levels correlate with tumor burden, meaning that higher levels suggest a larger tumor presence. Notably, extremely elevated levels (over 1,000 kilounits per liter) are particularly indicative of advanced pancreatic cancer. The test involves a straightforward blood sample collection and is processed through immunoassay techniques to quantify the protein presence. Though there are minimal risks associated with blood drawing, such as bleeding or infection, no special preparations are needed for this test. Normal levels of CA 19-9 are generally considered to be between 0–40 kilounits per milliliter, with values exceeding this threshold indicating potential health concerns.
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CA 19-9 test
ALSO KNOWN AS: Carbohydrate antigen 19-9, cancer antigen 19-9
DEFINITION: CA 19-9 is a glycolipid (carbohydrate-containing fat) characterized glycoprotein (carbohydrate-containing protein, or mucin). It is similar to the type A blood group protein, with additional sialic acid residues. CA 19-9 is found in normal fetal cells as well as in the pancreas, salivary ducts, gastric and colonic epithelium, pancreatic and gastric fluid, saliva, and meconium (first stool of a newborn). It is normally removed from circulation by the biliary system. Serum/plasma levels are determined by immunoassay.
Cancers diagnosed or treated: CA 19-9 is elevated in patients with gastrointestinal tract carcinoma, including cancer of the pancreas, stomach, colon, and ovaries. Abnormally high values may also be detected in conditions such as acute pancreatitis, cirrhosis, cholecystitis, biliary obstruction, gastric ulcer, pulmonary disease, and chronic hepatitis C, as well as in patients who smoke.
Why performed: Because CA 19-9 is not sensitive or specific enough to be used as a screening test, its primarily utility is as a tumor marker for monitoring response to therapy and recurrence in pancreatic cancer patients. It can also be helpful for early cancer patients as a means of detection prior to the cancer's spreading. Levels are typically proportional to the tumor burden (mass), with higher levels of CA 19-9 indicative of the presence of a larger tumor. Very elevated levels, defined as more than 1,000 kilounits per liter (kU/L), are highly specific for pancreatic cancer and indicate very advanced disease.
Patient preparation: No special patient preparation is required for accurate CA 19-9 analysis.
Steps of the procedure: A blood sample is collected, typically by venipuncture. The collected serum (or plasma) is tested by immunoassay, which involves capturing CA 19-9 present in the sample by means of monoclonal anti-CA 19-9 antibodies. A second, detection (radiolabeled) antibody is then introduced, which subsequently binds to the CA 19-9/anti-CA 19-9 complex. The addition of a substrate results in a detectable signal, the level of which is directly proportional to the amount of the CA 19-9 present in the sample.
After the procedure: Pressure should be applied to the venipucture site in order to avoid the development of a hematoma.
Risks: The risks of venipuncture are slight but include excessive bleeding, fainting, hematoma, and infection (always a slight risk any time the skin is broken).
Results: Although each laboratory establishes reference intervals based on the local, normal population, a basic interpretive guideline places normal at 0–40 kilounits per milliliter (kU/mL) and elevated at more than 40 kU/mL.
Bibliography
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