Laboratory Evaluation of Magnesium Status. Renal Function and Free Intracellular Magnesium Concentration

In summary, magnesium plays an essential role in both extracellular and intracellular metabolism. Even though biologists recognize the importance of magnesium, clinicians often are unaware of the frequency and significance of magnesium disturbances. Some clinicians recommend routine measurement of magnesium when other electrolyte analyses are required for the care of patients. Others have reported a high frequency of hypomagnesemia in hospitalized patients, but the clinical significance of this observation was not evident. Patients with coexisting hypokalemia of any cause require particular attention however, and it is important to assess magnesium status in that setting. The assessment of magnesium status is difficult because of the distribution of magnesium within the intracellular compartment. The majority of body magnesium is located within soft and hard tissues and most intracellular magnesium is complexed and not available for measurement. Accordingly, no single determination is available to accurately assess magnesium status. The simplest and most useful approach is the determination of serum magnesium and renal magnesium clearance and interpretation of these parameters in light of complete history and clinical evaluation of the patient. Accordingly, one combines the laboratory assessment with the clinical evaluation. Other tests, such as determination of serum and intracellular free Mg2+ activity by either fluorescent or 31P-NMR techniques, are not particularly useful in the routine laboratory. These approaches currently are being used on an experimental basis to assess the role of magnesium in health and disease, which may lead to better indices of clinical evaluation in the future.