What is the significance of a magnesium level of 0.61 mmol/L in an 86-year-old female, indicating hypomagnesemia?

From the Guidelines

A magnesium level of 0.61 mmol/L in an 86-year-old female indicates mild hypomagnesemia that requires treatment.

Treatment Recommendations

• I recommend oral magnesium supplementation with magnesium oxide 12 mmol at night, as suggested by the guidelines for management of patients with a short bowel 1.
• For this elderly patient, it is essential to correct water and sodium depletion, which can lead to secondary hyperaldosteronism, as this can exacerbate hypomagnesemia 1.
• If she has significant symptoms (muscle cramps, weakness, arrhythmias) or cannot tolerate oral supplements, consider IV magnesium sulfate, although the exact dosage is not specified in the provided guidelines.

Important Considerations

• Magnesium is essential for many enzymatic reactions in the body, including neuromuscular function, cardiac rhythm, and bone health, making its supplementation crucial, especially in elderly patients 1.
• It is also important to investigate potential causes of hypomagnesemia, including diuretic use, poor dietary intake, malabsorption, alcoholism, or diabetes.
• Monitoring her renal function before supplementation is necessary, as magnesium is primarily excreted by the kidneys and dosage adjustment may be needed with impaired kidney function.

From the FDA Drug Label

Normal plasma magnesium levels range from 1.5 to 2.5 mEq/L. To convert the given value of 0.61 mmol/L to mEq/L, we need to know that 1 mmol/L of magnesium is equivalent to 0.5 mEq/L (since the valence of magnesium is +2 and its molar mass is approximately 24.3 g/mol, with 1 equivalent being the amount of an ion that supplies or reacts with 1 mole of hydrogen ions, and for magnesium, 1 mole = 2 equivalents). Given that, 0.61 mmol/L * 2 = 1.22 mEq/L (or approximately 0.61 mmol/L * 2.06 if using atomic mass for more precise conversion, but for simplicity, we'll use the direct relationship for clinical purposes). The patient's magnesium level is below the normal range. Hypomagnesemia is present, as the level is less than 1.5 mEq/L. Symptoms may include muscle irritability, clonic twitching, and tremors, and the patient may be at risk for hypocalcemia and hypokalemia. Given the patient's age (86 years old) and low magnesium level, parenteral magnesium therapy may be considered to repair the plasma deficit and alleviate symptoms 2.

From the Research

Definition and Diagnosis of Hypomagnesemia

• Hypomagnesemia is defined as a serum magnesium level less than 1.8 mg/dL (< 0.74 mmol/L) 3
• The patient's magnesium level of 0.61 mmol/L falls below this threshold, indicating hypomagnesemia

Causes and Clinical Consequences of Hypomagnesemia

• Hypomagnesemia may result from inadequate magnesium intake, increased gastrointestinal or renal losses, or redistribution from extracellular to intracellular space 3
• Increased renal magnesium loss can result from genetic or acquired renal disorders 3
• Hypomagnesemia can have important clinical consequences, including ventricular arrhythmia and other life-threatening effects 3, 4
• The patient's age and sex do not necessarily determine the cause of hypomagnesemia, but older adults may be more susceptible to certain conditions that contribute to magnesium deficiency 5, 6

Evaluation and Management of Hypomagnesemia

• The first step to determine the likely cause of hypomagnesemia is to measure fractional excretion of magnesium and urinary calcium-creatinine ratio 3
• Asymptomatic patients should be treated with oral magnesium supplements, while parenteral magnesium should be reserved for symptomatic patients with severe magnesium deficiency (< 1.2 mg/dL) 3
• Establishment of adequate renal function is required before administering any magnesium supplementation 3
• Certain medications, such as proton pump inhibitors, can contribute to hypomagnesemia and should be considered in the patient's medical history 5