From the Guidelines
The correct method for Carbohydrate Antigen 19-9 (CA 19-9) determination involves a blood test that should be conducted after an overnight fast to ensure accurate results, with a healthcare professional drawing approximately 5-10 mL of blood from a vein, typically in the arm, using standard venipuncture technique, and the sample should be collected in a serum separator tube and processed within 2-4 hours of collection 1.
Key Considerations for CA 19-9 Determination
- The test should be performed after an overnight fast to minimize potential interference from recent food consumption.
- Patients should avoid smoking and alcohol consumption for at least 24 hours before the test to ensure accurate results.
- Certain conditions like jaundice, pancreatitis, and inflammatory bowel disease can cause false elevations in CA 19-9 levels, while approximately 5-10% of the population lacks the Lewis antigen necessary to produce CA 19-9, leading to potential false negative results even in the presence of pancreatic cancer 1.
Interpretation of CA 19-9 Results
- Normal CA 19-9 levels are typically below 37 U/mL, though reference ranges may vary slightly between laboratories.
- The test is most valuable when used for monitoring treatment response or disease recurrence in patients with known pancreatic cancer rather than as a standalone diagnostic tool, as it has a significant value as a prognostic factor and can be used to measure disease burden and guide treatment decisions 1.
Clinical Application of CA 19-9 Determination
- A preoperative serum CA 19-9 level ≥500 UI/ml clearly indicates a worse prognosis after surgery, highlighting the importance of this marker in clinical decision-making 1.
- CA 19-9 determination should be part of a comprehensive diagnostic workup that includes imaging studies like computed tomography (CT) angiography and endoscopic ultrasound (EUS) to accurately stage pancreatic cancer and guide treatment planning.
From the Research
CA 19-9 Determination Methods
The correct method for Carbohydrate Antigen 19-9 (CA 19-9) determination involves using a commercial assay, such as the one from Roche Diagnostics 2 or the CA 19-9-MP-Mitsui kit 3. These assays typically use a sandwich enzyme immunoassay with mouse monoclonal antibodies to determine CA 19-9 levels in serum.
Assay Characteristics
- The CA 19-9 assay from Roche Diagnostics has an upper limit of normality of 37 U/ml 2.
- The CA 19-9-MP-Mitsui kit has excellent reproducibility, high sensitivity, and specificity for CA 19-9, with a coefficient of positive correlation of 0.92 compared to the Immunoclone CA 19-9 EIA kit 3.
- A cut-off value of 70 U/ml may be more suitable for diagnosing pancreatic and bile duct cancers, as it reduces false positive incidence, particularly in liver cirrhosis or hepatitis 3.
Sample Collection and Analysis
- Blood samples can be collected from peripheral veins or the portal vein to measure CA 19-9 concentration 4.
- CA 19-9 concentration in the portal blood may be significantly higher than in the peripheral blood, particularly in patients with malignant pancreatic tumors without metastases to the liver 4.
- Determining CA 19-9 concentration in both peripheral and portal blood may be a useful diagnostic tool for differentiating between malignant and inflammatory pancreatic tumors 4.
Clinical Applications
- CA 19-9 is a useful tumor marker for pancreatic adenocarcinomas, with a clear relationship with tumor location, stage, and resectability 2, 5.
- CA 19-9 levels can be used to monitor pancreatic and gastrointestinal cancer, but its application in screening is not recommended due to limited specificity and sensitivity 6.