Why is magnesium (Mg) level checked when hypokalemia is present?

From the Guidelines

Checking magnesium levels when potassium is low is crucial because magnesium deficiency can impede the correction of hypokalemia, as evidenced by the ESPEN guidelines on parenteral nutrition 1. When potassium levels are low, it is essential to assess magnesium levels as well, due to their interconnected roles in the body. Magnesium is necessary for the proper functioning of the sodium-potassium ATPase pump, which helps maintain intracellular potassium levels. A deficiency in magnesium can lead to impaired potassium transport into cells, making it challenging to correct hypokalemia.

• The relationship between magnesium and potassium is highlighted in the context of gastrointestinal losses, where both electrolytes are lost, and sodium depletion can lead to hyperaldosteronism, increasing renal retention of sodium at the expense of magnesium and potassium 1.
• Magnesium deficiency can also impair parathyroid hormone release, leading to calcium deficiency, which further complicates the clinical picture 1.
• To effectively manage hypokalemia, it is vital to correct sodium and water depletion first, followed by magnesium supplementation to bring serum levels into the normal range, as recommended in the ESPEN guidelines 1.
• Treatment may involve oral magnesium supplements, such as magnesium oxide, or intravenous magnesium sulfate in more severe cases, alongside appropriate potassium replacement, to ensure effective electrolyte repletion and better clinical outcomes.

From the FDA Drug Label

Hypocalcemia and hypokalemia often follow low serum levels of magnesium.

We check magnesium when potassium is low because hypokalemia often follows hypomagnesemia. In other words, low magnesium levels can lead to low potassium levels. Therefore, checking magnesium levels can help identify the underlying cause of hypokalemia. 2

From the Research

Magnesium and Potassium Relationship

• Magnesium plays a crucial role in maintaining potassium homeostasis, and its deficiency can lead to hypokalemia 3, 4.
• Hypomagnesemia can cause refractory hypokalemia, which can be corrected with magnesium therapy 3.
• Magnesium deficiency can increase distal potassium secretion, leading to hypokalemia, especially in the presence of increased distal sodium delivery or elevated aldosterone levels 4.

Clinical Implications

• Checking magnesium levels is essential when potassium is low, as magnesium deficiency can exacerbate hypokalemia and render it refractory to treatment 3, 4.
• Hypokalemia can have various causes, including decreased intake, renal losses, gastrointestinal losses, or transcellular shifts, and addressing the underlying cause is crucial for treatment 5, 6.
• Maintaining homeostasis of potassium and magnesium is critical in managing comorbid conditions, such as hypertension, diabetes, and congestive heart failure 7.

Diagnostic and Treatment Approaches

• Measuring magnesium concentration in the urine or using the parenteral magnesium load test can help detect magnesium deficiency 3.
• Treatment of hypokalemia depends on the underlying cause and may involve oral or intravenous potassium supplementation, as well as addressing the underlying condition 5, 6.
• Potassium-sparing diuretics and magnesium-sparing diuretics can be used to retain these ions and maintain homeostasis 7.