What is the usual range of Carbohydrate Antigen 19-9 (CA 19-9) in pancreatic cancer?

CA 19-9 Range in Pancreatic Cancer

CA 19-9 is elevated above 37 U/mL in approximately 80-85% of patients with pancreatic cancer, with significantly higher levels typically seen in advanced disease compared to early-stage disease. 1, 2

Normal Values and Elevation in Pancreatic Cancer

• Normal range: ≤37 U/mL (standard cutoff value)
• Elevation in pancreatic cancer:
  • Present in 81.5-90% of pancreatic cancer patients 2, 3
  • Levels vary significantly based on disease stage and tumor burden
  • Early/localized disease: Often moderately elevated (40-120 U/mL) 3
  • Advanced disease: Can reach extremely high values (thousands of U/mL) 2, 4

Factors Affecting CA 19-9 Levels

Tumor-Related Factors

• Tumor location: Highest levels in body of pancreas, lower in tail or uncinate process 2
• Tumor stage: Progressive increase with more advanced disease 2, 3
• Tumor differentiation: Lower levels in poorly differentiated carcinomas 3
• Metastatic site: Highest with liver metastases 2

Patient-Related Factors

• Lewis antigen status: 7-10% of the population (Lewis-negative individuals) cannot produce CA 19-9, resulting in false-negative results 1, 5
• Biliary obstruction: Can cause false-positive elevation, with levels correlating to bilirubin levels 1, 5
• Resectability: Significantly lower concentrations in resectable tumors 2

Clinical Significance of CA 19-9 Levels

Diagnostic Value

• Not recommended for primary diagnosis (sensitivity 79-81%, specificity 82-90%) 5
• Values >500 U/mL indicate worse prognosis after surgery 1
• Values >120 U/mL highly suggestive of malignancy versus chronic pancreatitis 3

Prognostic Value

• Postoperative normalization: Strong positive prognostic indicator 1, 6
  • Patients with normalization after resection show significantly better survival
  • Failure to normalize postoperatively predicts worse disease-free survival 4
• Response to treatment:
  • Decline of >25% during chemotherapy predicts improved survival in advanced disease 4
  • Serial monitoring every 1-3 months recommended during treatment 5

Pitfalls and Caveats

• CA 19-9 should not be used alone for screening or diagnosis 5
• False positives occur with:
  • Benign biliary obstruction 1
  • Acute cholangitis (can reach extremely high values >9,000 U/mL) 7
  • Chronic pancreatitis (though usually <120 U/mL) 3
• False negatives occur in:
  • Lewis-negative individuals 1
  • Some poorly differentiated pancreatic carcinomas 3
• CA 19-9 measurements using different testing methods cannot be directly compared 1

Monitoring Recommendations

• Measure CA 19-9 after biliary decompression is complete (if jaundice present) 1
• Obtain baseline levels before treatment initiation 1
• Monitor every 1-3 months during treatment 5
• Rising pattern over time suggests recurrence, even with negative imaging 5
• Always interpret CA 19-9 results alongside clinical and imaging findings 5