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The effect of magnesium supplementation on vascular calcification in chronic kidney disease—a randomised clinical trial (MAGiCAL-CKD): essential study design and rationale
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  • Iain Bressendorff, Ditte Hansen, Morten Schou, Charlotte Kragelund and Lisbet Brandi
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    Changes to Statistical Plan
    • Iain Bressendorff, Nephrology Fellow Nordsjællands Hospital, Hillerød, Denmark
    • Other Contributors:
      • Ditte Hansen, Consultant Nephrologist
      • Morten Schou, Consultant Cardiologist
      • Charlotte Kragelund, Consultant Cardiologist
      • Lisbet Brandi, Consultant Nephrologist

    We hereby write to inform the readers of changes to the statistical plan for our clinical trial MAGiCAL-CKD, which we have previously published in BMJ Open. At the time of writing, the trial is still on-going and the data set has not been unblinded. Thus, any changes to the statistical plan at this time will not compromise the integrity of the trial design.
    The purpose of the MAGiCAL-CKD trial is to examine the effect of magnesium (Mg) supplementation on coronary artery calcification (CAC) score in patients with chronic kidney disease. The original statistical plan was to analyse the change in CAC score from week 0 to week 52 (delta CAC score) and compare the delta CAC score between the two treatment groups. The choice of delta CAC as the primary endpoint (and not the between-group difference in CAC score at week 52) was made due to the potential for an imbalance in CAC score between the two treatment groups at week 0. The delta CAC was thought to better account for any baseline imbalance. However, since the publication of the trial protocol we have become aware that this methodology is flawed and that the correct analysis is to perform an analysis of covariance (ANCOVA) of CAC score between the two treatment groups at week 52 adjusted for CAC score, age and prevalent diabetes mellitus (yes/no) at week 0. Therefore, the ANCOVA test will be applied to analyse the primary endpoint. Essentially, we are examining the same scientific question, but using better methodology...

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    Conflict of Interest:
    None declared.