BACKGROUND: Interassay variability is one of the challenging issues of routine clinical laboratory practice. Commercial plasma cortisol immunoassays are also subject to this issue. In this study, we intended to evaluate the interchangeability of cortisol results of three widely used immunoassay systems. METHODS: The cortisol values of 150 serum samples measured by three immunoassay systems, Beckman Coulter DXI 800, Roche Modular E170, and Siemens Immulite 2500, were compared. RESULTS: A degree of proportional biases was observed between all three methods; DXI 800 showed the worst biases with the other two systems (slope values 0.67 and 0.77 with E170 and Immulite 2500, respectively). DXI 800 showed poor agreement with other methods (CCC: 0.83 and 0.87, respectively). There was a moderate agreement between E170 and Immulite 2500 (CCC: 0.92). CONCLUSIONS: All three methods showed a degree of variability among themselves. DXI 800 results were not interchangeable with the other two systems.
BACKGROUND: Interassay variability is one of the challenging issues of routine clinical laboratory practice. Commercial plasma cortisol immunoassays are also subject to this issue. In this study, we intended to evaluate the interchangeability of cortisol results of three widely used immunoassay systems. METHODS: The cortisol values of 150 serum samples measured by three immunoassay systems, Beckman Coulter DXI 800, Roche Modular E170, and Siemens Immulite 2500, were compared. RESULTS: A degree of proportional biases was observed between all three methods; DXI 800 showed the worst biases with the other two systems (slope values 0.67 and 0.77 with E170 and Immulite 2500, respectively). DXI 800 showed poor agreement with other methods (CCC: 0.83 and 0.87, respectively). There was a moderate agreement between E170 and Immulite 2500 (CCC: 0.92). CONCLUSIONS: All three methods showed a degree of variability among themselves. DXI 800 results were not interchangeable with the other two systems.