['The variety of LC-MS/MS methods measuring total 25(OH)D used today is vast and the comparability among these methods is still not well assessed.', 'Here, we performed a comparison in samples of healthy donors between the currently routinely used 25(OH)D LC-MS/MS methods in the Netherlands and the Ghent University reference measurement procedure to address this issue (n=40). Additionally, an interlaboratory comparison in patient serum samples assessed agreement between the Dutch diagnostic methods (n=37).', 'The overall correlation of the routine methods for 25(OH)D'] Do various calibration procedures result in optimal standardization of routinely used 25 ( OH ) D ID-LC-MS/MS methods?