Extent of bilirubin interference with Beckman creatinine methods

BACKGROUND: The aim of the study was to determine the extent of bilirubin interference on two different Beckman-Coulter creatinine methods used on the CX5 PRO/DxC 600 and the DxC 800 systems, respectively. METHODS: The Beckman methods were compared with a high-performance liquid chromatography (HPLC) method using 104 patient samples with creatinine concentrations <133 micromol/L and bilirubin concentrations of between 30 and 802 micromol/L. RESULTS: The linear regression analysis calculations expressing the relationship between bilirubin concentration and the observed difference between the Beckman and HPLC creatinine methods are: DxC800 creatinine M (modular or cup) method: r(2) 0.217, slope -0.023 and intercept 6.43; and DxC600 method: r(2) 0.7324, slope -0.0882 and intercept 12.01. CONCLUSIONS: There is significantly greater interference by bilirubin on the CX5 PRO/DxC 600 method, which can lead to inaccuracy in the calculation of the estimated glomerular filtration rate by the Modification of Diet in Renal Disease equation.