Can lupus elevate Carbohydrate Antigen 19-9 (CA 19-9) levels?

Can Lupus Elevate CA 19-9 Levels?

Yes, systemic lupus erythematosus (SLE) can cause elevated CA 19-9 levels, with studies showing that approximately 7.5-31.6% of lupus patients may have elevated CA 19-9 without any underlying malignancy. 1, 2, 3

Understanding CA 19-9 and Its Limitations

• CA 19-9 is a tumor-associated antigen originally defined by a monoclonal antibody produced from murine spleen cells immunized with human colorectal cancer cell lines 4, 5
• It exists in tissue as an epitope of sialylated Lewis A blood group antigen 4, 5
• Approximately 5-10% of the population is Lewis antigen-negative and cannot produce CA 19-9, making testing ineffective in these individuals 4, 5
• CA 19-9 is not specific for malignancy and can be elevated in multiple benign conditions 6, 7

CA 19-9 Elevation in Autoimmune Diseases

• Studies have demonstrated that CA 19-9 can be elevated in patients with various rheumatic diseases, including SLE, without evidence of malignancy 8, 2
• In one study, 31.6% of patients with SLE had elevated CA 19-9 levels 2
• Another study found that 7.5% of SLE patients had CA 19-9 levels above the normal cut-off value (37 U/ml) 3
• The CA 19-9 antigen found in sera from patients with rheumatic diseases has been shown to have the same molecular weight as that found in patients with pancreatic cancer 2

Clinical Significance of CA 19-9 Elevation in Lupus

• In SLE patients, CA 19-9 elevation may occur alongside other tumor markers, including CEA (32.5%), CA125 (15.0%), and CA72-4 (15.0%) 3
• Some studies suggest that elevated CA 19-9 in lupus patients may be associated with specific organ involvement, particularly lung disease 8
• CA 19-9 levels in benign conditions (including SLE) are typically significantly lower than those seen in malignant conditions 1

Differential Diagnosis When CA 19-9 is Elevated

• When elevated CA 19-9 is found in a patient with lupus, consider:
  • Lupus itself as the cause of elevation 1, 2
  • Pancreatic or biliary tract malignancy (primary concern with very high levels) 4, 6
  • Other gastrointestinal malignancies (colorectal, gastric) 5, 1
  • Benign hepatobiliary conditions 4, 6
  • Lung involvement in connective tissue disease 8
  • Chronic pancreatitis 8

Management Approach for Elevated CA 19-9 in Lupus Patients

• Interpret CA 19-9 levels in the context of clinical presentation and other findings 6
• Consider that moderate elevation (<100 U/ml) is less specific for malignancy 6
• If levels are significantly elevated (>100 U/ml) or there are concerning symptoms:
  • Evaluate for biliary obstruction with ultrasound as first-line investigation 9, 6
  • Consider MRI with MRCP for more detailed evaluation of the pancreaticobiliary system 9, 6
  • Monitor CA 19-9 levels after treating any identified biliary obstruction, as persistent elevation after decompression is more concerning for malignancy 6

Important Caveats

• CA 19-9 is not recommended as a screening test for malignancy due to inadequate sensitivity and specificity 4, 5
• False positive elevations can occur in many benign conditions, including SLE 1, 2
• CA 19-9 measurements using different testing methods cannot be directly compared 6
• Always interpret CA 19-9 levels in the context of the patient's clinical presentation 6, 1