The accuracy of the CA 19-9 tumor marker varies depending on the specific medical context and how accuracy is measured. Based on a significant systematic review, its performance for diagnosing pancreatic ductal adenocarcinoma (PDAC) in symptomatic patients shows moderate accuracy.
Specifically, a systematic review by Goonetilleke et al. [13] analyzed data from 2283 symptomatic patients. Using the largely standardized threshold level of 37-40 U/mL for elevated CA 19-9, the study reported the following accuracy metrics for its diagnostic value in PDAC:
CA 19-9 Accuracy Metrics (Goonetilleke et al. Systematic Review)
| Metric | Value |
|---|---|
| Sensitivity | 79.0% |
| Specificity | 82.0% |
| PPV (Positive Predictive Value) | 72.0% |
| NPV (Negative Predictive Value) | 81.0% |
Understanding the Metrics
- Sensitivity: The ability of the test to correctly identify patients with the disease (PDAC). A 79.0% sensitivity means it correctly identifies about 79 out of 100 people who actually have PDAC.
- Specificity: The ability of the test to correctly identify patients without the disease. An 82.0% specificity means it correctly identifies about 82 out of 100 people who do not have PDAC.
- Positive Predictive Value (PPV): The probability that a patient actually has the disease, given a positive test result. A 72.0% PPV means that if a patient's CA 19-9 is elevated above the threshold, there is about a 72% chance they have PDAC in this specific population (symptomatic patients).
- Negative Predictive Value (NPV): The probability that a patient does not have the disease, given a negative test result. An 81.0% NPV means that if a patient's CA 19-9 is below the threshold, there is about an 81% chance they do not have PDAC in this specific population.
These figures indicate that while CA 19-9 is a useful tool, it is not perfectly accurate on its own and should be interpreted alongside other clinical information and diagnostic tests.
