From the Guidelines
CA 19-9 should not be used as a screening test for pancreatic cancer due to its limited sensitivity and specificity for early detection in asymptomatic individuals. The most recent and highest quality study, 1, published in 2017, highlights the importance of biomarkers for early detection of pancreatic cancer, but also emphasizes the limitations of CA 19-9 as a screening tool. According to this study, CA 19-9 has a low positive predictive value, making it a poor biomarker for screening, and its levels can be falsely positive in cases of biliary infection, inflammation, or biliary obstruction.
Some of the key limitations of CA 19-9 as a screening test include:
- Elevated levels in non-cancerous conditions, such as pancreatitis, cholangitis, and other gastrointestinal disorders, leading to false positive results and unnecessary invasive procedures
- Approximately 5-10% of the population cannot produce CA 19-9 due to Lewis antigen negativity, resulting in false negative results even when cancer is present
- CA 19-9 levels typically only become significantly elevated in advanced stages of pancreatic cancer, when treatment options are already limited
- The low prevalence of pancreatic cancer in the general population means that even a test with good performance characteristics would yield many false positives
Instead, CA 19-9 is more appropriately used for:
- Monitoring treatment response in patients with established pancreatic cancer diagnoses
- Diagnostic workup in symptomatic patients with suspected pancreatic disease, always in conjunction with imaging studies and clinical evaluation, as recommended by 1 and 1.
It is essential to consider the limitations and potential biases of the studies, including the fact that the studies were published in different years and may have different levels of evidence. However, the most recent and highest quality study, 1, provides the strongest evidence for the limitations of CA 19-9 as a screening test.
From the Research
Limitations of CA 19-9 as a Screening Test
- CA 19-9 is not useful for screening pancreatic cancer in the asymptomatic general population due to its poor positive predictive value 2, 3, 4
- The test has a low sensitivity and specificity for diagnosing pancreatic cancer in asymptomatic individuals, making it unreliable for screening purposes 5, 3, 4
- False negative results can occur in individuals with the Lewis (a-b-) genotype, which can lead to missed diagnoses 2, 3, 4
- False positive results can occur in patients with benign diseases, such as obstructive jaundice, which can lead to unnecessary further testing and anxiety 2, 3, 4
Clinical Utility of CA 19-9
- CA 19-9 is useful for diagnosing pancreatic cancer in symptomatic patients, with a sensitivity and specificity of 79-81% and 82-90%, respectively 5, 3, 4
- The test can provide prognostic information, with elevated levels associated with poorer survival outcomes 6, 3, 4
- CA 19-9 levels can be used to monitor response to treatment and predict post-operative recurrence 3, 4
Alternative Uses of CA 19-9
- CA 19-9 may be useful as a screening indicator of pancreatic cancer in asymptomatic patients with new-onset diabetes, particularly those with high serum bilirubin levels 6
- The test can be used to evaluate the resectability of pancreatic cancer, with levels <100 U/mL suggesting likely resectable disease 3, 4