CA 19-9 Tumor Marker Interpretation

Test Definition and Methodology

CA 19-9 is a sialylated Lewis A blood group antigen commonly expressed and shed in pancreatic, hepatobiliary, and gastrointestinal diseases, with multiple commercial assay methods available for quantitation, but results from different testing methods cannot be directly compared or extrapolated, as stated by the National Comprehensive Cancer Network 3, 4
The American College of Clinical Oncology recommends interpreting CA 19-9 levels with caution in the context of clinical presentation and imaging findings, as it can be elevated in both malignant and benign conditions 1, 2

5-10% of the population are Lewis antigen-negative and cannot produce CA 19-9, resulting in undetectable or very low levels even in the presence of malignancy, according to the Journal of Clinical Oncology 1, 2, 5
Benign biliary obstruction can cause significantly elevated CA 19-9 levels, as reported by the National Comprehensive Cancer Network 3, 4, 5
Cholangitis and biliary infections frequently elevate CA 19-9 levels, as stated by Hepatology 6, 7

The National Comprehensive Cancer Network does not recommend screening asymptomatic populations with CA 19-9 due to a positive predictive value of 0.5-0.9% 1, 2
CA 19-9 levels should be measured after complete biliary decompression when evaluating for pancreatic pathology, as recommended by the National Comprehensive Cancer Network 3, 4
The American College of Clinical Oncology suggests using CA 19-9 as a diagnostic aid in symptomatic patients when combined with imaging findings, with a sensitivity of 79-81% and specificity of 82-90% 10

Elevated CA 19-9 alone does not establish a diagnosis of malignancy and must be correlated with clinical presentation, imaging studies, and/or tissue diagnosis, as stated by the Journal of Clinical Oncology 1, 2
In primary sclerosing cholangitis, a cut-off of 129-130 U/mL provides optimal sensitivity and specificity for cholangiocarcinoma detection, according to Hepatology and Clinical Gastroenterology and Hepatology 6, 7, 9