Biomarkers for assessing magnesium status.

Magnesium (Mg), the second most abundant intracellular cation, plays critical roles in over 600 enzymatic reactions and influences multiple physiological systems, including endocrine, nervous, cardiovascular, and immune function. Despite its manifold importance, assessing Mg status remains a significant challenge in clinical practice and epidemiological research due to the predominantly intracellular distribution of Mg, with less than 1-2 percent present in blood and extracellular fluid. This chapter examines current measures of Mg status (serum/plasma, free ionized, urine), intracellular measurements (red blood cells, leukocytes, platelets), non-invasive sampling (hair, nails), and functional assessment (Mg loading test, balance studies). We discuss the advantages and limitations of each approach, highlighting that no single biomarker reliably reflects whole-body Mg status. The chapter also addresses the development of novel approaches, including the Mg Depletion Score (MDS), genetic biomarkers involving Mg transport proteins (TRPM6, TRPM7, CNNM family, MAGT1), and specialized applications in pregnancy and preeclampsia. The physiological mechanisms of Mg homeostasis involving intestinal absorption, renal regulation, and bone storage are examined to provide context for biomarker interpretation. Current evidence suggests that serum Mg, while widely used, may not detect subclinical deficiency, and that combination approaches incorporating functional tests and clinical factors may provide superior diagnostic accuracy. Future research should focus on developing sensitive, accurate, and minimally invasive biomarkers that can effectively guide clinical decision-making and support population health surveillance for Mg-related non-communicable diseases.