Identifying High-Yield Groups for the Detection of Low Serum Magnesium in Diabetes: A Nationally Representative Study of Korean Adults

Background/Objectives: Diabetes predisposes to magnesium deficiency, yet serum magnesium is not routinely measured. Using an unselected national sample, I sought a practical criterion for predicting which adults with diabetes are more likely to have low serum magnesium (<0.75 mmol/L) and examined clinical correlates. Methods: I analyzed 5798 adults aged ≥19 years from the 2024 Korea National Health and Nutrition Examination Survey using survey-weighted methods. Diagnostic yield was the proportion tested with low serum magnesium. Criteria combining guideline-based glycated hemoglobin (HbA1c) and estimated glomerular filtration rate (eGFR) thresholds were compared by diagnostic yield and Youden index. Results: Low serum magnesium occurred in 10.7% of adults with diabetes versus 2.4% without diabetes; those with diabetes accounted for 41.0% of all cases. Among criteria with a Youden index of at least 0.20, HbA1c ≥8% or eGFR <60 mL/min/1.73 m2 required the fewest tests and had the highest diagnostic yield (21.7%). This group comprised 17.6% of adults with diabetes but 35.7% of cases. Low serum magnesium was associated with HbA1c ≥8% (odds ratio 3.10; 95% confidence interval 1.64–5.84) and albuminuria (2.10; 1.17–3.75), largely consistently across sensitivity analyses. Exploratory analyses also identified associations with depressive symptoms and fatigue. Dietary magnesium density did not differ by magnesium status. Conclusions: Testing adults with diabetes who had HbA1c ≥8% or eGFR <60 mL/min/1.73 m2 identified low serum magnesium about twice as efficiently as testing all adults with diabetes.