Elevated CA19-9 in IgG4-related disease

BackgroundIgG4-related disease (IgG4-RD) is an inflammatory disease that can clinically mimic pancreatic and hepatobiliary cancer. Serum carbohydrate antigen 19-9 (CA19-9) is a tumour marker that is frequently used to aid in the diagnosis of biliary cancer. There have been reported cases that patients with IgG4-RD also have elevated CA19-9.MethodsThis study has two components, first, a quality assurance component that observes paired IgG4 and CA19-9 measurements from patients with unknown diagnoses were compared to determine if serum IgG4 interferes with CA19-9 measurement. In addition, a mixing study is used to investigate if high levels of IgG4 interfered with CA19-9 measurements. Second, a retrospective chart review was performed to compare patients diagnosed with IgG4-RD with normal versus elevated CA19-9.ResultsAmong 487 unique individuals with paired measurements, no association between CA19-9 and serum IgG4 was found. Mixing studies revealed no interference. Among 20 patients with IgG4-RD, 11 had elevated CA19-9 (median 150 kU/L) and nine had normal CA19-9. There was no difference in bilirubin between the two groups (63.2 µmol/L vs 39.4 µmol/L, <i>P</i> = .47).ConclusionThere is no relationship between CA19-9 and serum IgG4. Patients with IgG4-RD and elevated CA19-9 did not have higher bilirubin than those with normal CA19-9. Together, these results suggest that elevated CA19-9 in IgG4-RD may be related to the disease rather than to interference from high serum IgG4 or from biliary obstruction.