Comparison of three immunoassays for CA 19-9

BackgroundCarbohydrate antigen (CA) 19-9 is a valuable tumor marker for gastrointestinal (GI) cancers, but results obtained by different assays vary and a change of method during follow-up may cause problems.MethodsWe determined CA 19-9 using Abbott i2000 Architect (CA 19-9XR assay), Roche Elecsys 2010 and Bayer Immuno 1 analyzers. Between-method correlation was studied in 610 serum samples from patients with GI disease. Clinical performance was compared using samples from 68 patients with benign GI diseases and 106 cancer patients. Reference intervals for the Abbott and Roche methods were determined (n = 315).ResultsThe Architect assay measured significantly lower concentrations than the other assays in controls and benign disease (p < 0.0001), and the upper reference limit was lower (26 kU/l) than for Elecsys (36 kU/l). The area under curve (AUC) for discrimination between benign disease and pancreatic cancer was significantly larger (0.90; 95% CI 0.83–0.98) than for Elecsys (0.78) and Immuno 1 (0.76). However, for all assays a cut-off of 37 kU/l provided optimal separation between benign and malignant disease.ConclusionsThe Architect CA 19-9XR assay measures lower concentrations than the other two assays in benign conditions. Thus it provides the best discrimination between benign and malignant GI disease.