Serum and Urinary Magnesium Status in Asian CKD Patients and Healthy Controls: A Cross-Sectional Analysis

Magnesium is an essential dietary mineral, and low magnesium status has been associated with adverse cardiometabolic and renal outcomes. In chronic kidney disease (CKD), the prevalence of magnesium deficiency remains uncertain because serum magnesium alone may not accurately reflect overall magnesium status. We aimed to characterize magnesium status in a multi-ethnic Asian CKD cohort compared with healthy participants using combined serum and 24-h urinary magnesium (24U-Mg) measurements.

This cross-sectional observational study included 232 adults with CKD and 103 healthy participants. Serum magnesium and 24-h urinary magnesium excretion were measured concurrently. Magnesium deficiency was defined as serum magnesium ≤0.75 mmol/L; probable magnesium deficiency was defined as serum magnesium 0.76-0.85 mmol/L with 24U-Mg ≤ 3.29 mmol/day; and possible magnesium deficiency was defined as either normal serum Mg with low 24U-Mg ≤ 1.65 mmol/day or serum Mg 0.76-0.85 mmol/L with 24U-Mg > 3.29 mmol/day. Associations with age, sex, body mass index, diabetes, blood pressure, and kidney function were examined.

CKD participants had lower mean serum magnesium (0.86 vs. 0.90 mmol/L, p < 0.001) and lower 24U-Mg (2.50 vs. 2.93 mmol/day, p = 0.006) compared with healthy participants. Using the proposed combined serum and 24U-Mg criteria, magnesium deficiency was present in 13.8% of CKD participants and 0% of healthy participants, while probable deficiency was observed in an additional 25.8% of CKD and 16.5% of healthy participants. Multivariate analysis demonstrated that CKD, older age, high BMI, and diabetes status were independently associated with lower serum magnesium levels, and female sex was associated with lower serum and urinary magnesium in healthy participants.

Magnesium deficiency is common in non-dialysis CKD patients and is frequently not identified by serum magnesium alone. Combined assessment using serum and urinary magnesium may better identify individuals at risk of magnesium deficiency and inform future prospective studies in CKD.