Magnesium levels in critically ill patients. What should we measure?

Area of Science:

• Biochemistry
• Critical Care Medicine
• Clinical Chemistry

Background:

• Magnesium is vital for cellular functions, and its dysregulation is common in critical illness.
• Assessing magnesium status in critically ill patients is complex due to various measurement methods.
• The relationship between extracellular, intracellular magnesium, and clinical outcomes requires further clarification.

Purpose of the Study:

• To investigate the relationship between serum ionized magnesium, total magnesium, and albumin in critically ill patients.
• To evaluate the role of extracellular and intracellular magnesium in predicting clinical outcomes.
• To determine the reliability of calculated ionized magnesium versus direct measurement.

Main Methods:

• Serum total magnesium, ionized magnesium, albumin, and intracellular magnesium (in mononuclear cells and erythrocytes) were measured in 115 critically ill patients.
• APACHE II scores and 1-month mortality were recorded for outcome assessment.
• Statistical analyses were performed to assess correlations and associations.

Main Results:

• 51.3% of patients had low serum total magnesium; however, 71% of these had normal serum ionized magnesium.
• No patients exhibited intracellular magnesium deficiency.
• Serum total magnesium and ionized magnesium showed weak correlation; serum albumin negatively correlated with ionized magnesium.
• No significant association was found between low extracellular or intracellular magnesium and clinical outcomes.

Conclusions:

• Hypomagnesemia in critically ill patients is dependent on the magnesium fraction measured.
• Low magnesium levels, particularly when calculated, may be an epiphenomenon rather than a predictor of outcome.
• Direct measurement of serum ionized magnesium is essential for accurate assessment in critically ill patients.