The Magnesium (Serum) blood test measures the level of magnesium circulating in the bloodstream. Magnesium is an essential mineral that plays a critical role in hundreds of biochemical reactions within the body, including energy production, muscle contraction, nerve transmission, and regulation of heart rhythm.

Serum magnesium reflects the amount of magnesium available in the blood at the time of testing. Although only a small proportion of the body’s total magnesium is found in the blood, serum levels provide useful information when assessing acute imbalances or monitoring known magnesium disturbances.

Low serum magnesium levels may occur due to inadequate dietary intake, gastrointestinal disorders affecting absorption, excessive losses through the kidneys, or certain medications such as diuretics. Symptoms can include muscle cramps, weakness, fatigue, tremors, palpitations, and, in more severe cases, abnormal heart rhythms.

High magnesium levels are less common but may occur in people with kidney impairment or excessive supplementation. Elevated levels can cause nausea, low blood pressure, slowed reflexes, and cardiac complications.

The serum magnesium test is often requested when investigating electrolyte imbalances, neuromuscular symptoms, cardiac arrhythmias, or as part of routine metabolic assessment. Results are interpreted alongside other electrolytes and clinical findings.