Chapter 3 56 a slope of 1.077 (95% CI: 1.019; 1.142) (Figure 1A). A Bland-Altman plot showed a systematic bias of 0.44 mmol/L with iIEM being slightly higher as compared to dIEM (Figure 1B). When expressed as magnesium per 1012 cells, a higher correlation was observed between dIEM and iIEM (r = 0.75). Ordinary linear regression analysis produced an intercept of 0.078 (0.070; 0.085) and a slope of 0.836 (95% CI: 0.800; 0.872) and Passing-Bablok regression produced an intercept of 0.015 (95% CI: 0.005; 0.023) and a slope of 1.157 (95% CI: 1.109; 1.210) (Figure 1C). A Bland-Altman plot showed a systematic bias of 0.04 mmol/1012 cells with iIEM being slightly higher as compared to dIEM (Figure 1D). Correlations between dIEM, iIEM, plasma magnesium and urinary magnesium excretion We found a positive correlation between plasma magnesium and dIEM (r=0.18, P<0.001) (Figure 2A). We observed no correlation between 24-h urinary magnesium excretion and dIEM (r=-0.002, P=0.94) (Supplemental Figure 2A). Similar correlations were found between plasma magnesium and iIEM (r=0.14, P<0.001) (Figure 2B) and 24-h urinary magnesium excretion and iIEM (r=0.00, P=1.00) (Supplemental Figure 2B). Finally, 24-h urinary magnesium excretion was not correlated with plasma magnesium (r=0.05, P=0.07) (Supplemental Figure 2C). Determinants of dIEM and iIEM Determinants of dIEM and iIEM are presented in Table 2. HbA1c was inversely associated with dIEM after adjustment for potential confounders. Among lipids, we found that higher total- and LDL cholesterol and triglyceride concentrations were associated with higher dIEM, even after adjustment for potential confounders. Also, higher plasma concentrations of sodium and potassium were associated with higher dIEM. iIEM was positively associated with BMI, waist circumference, total- and LDL cholesterol, triglycerides, plasma sodium and potassium. Subgroup analyses are presented in Table 3. Higher age was associated with higher iIEM concentrations in females. Similar associations were found between the determinants and iIEM and dIEM expressed as mmol per liter packed blood cells (Supplemental Table 3).
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