Magnesium, Blood

What is Magnesium, Blood?

A mineral involved in muscle, nerve, and heart function.

Magnesium is involved in muscle contraction, nerve signaling, and heart rhythm. Blood (serum) magnesium reflects less than 1% of the body's total magnesium — most is stored in bone and muscle — so a normal blood level doesn't always rule out a body-wide shortfall.

Tests often checked alongside this

• Calcium — magnesium affects how the body regulates calcium
• Potassium — deficiencies in the two often occur together
• PTH (parathyroid hormone) — low magnesium can disrupt PTH release and cause low calcium
• RBC Magnesium — may better reflect stored magnesium than a standard blood test

How this can show up in how you look and feel

• Low magnesium can be associated with muscle cramps or twitches
• Some people notice fatigue or general weakness
• Irregular heartbeat or palpitations can be associated with more significant deficiency
• Sleep disturbances or irritability are sometimes reported, though evidence for this link is less established than for cramps or fatigue

What can affect this marker

• Diet and gut absorption
• Kidney function
• Alcohol use and certain medications
• Chronic diarrhea or vomiting

What to track over time

• Your trend across repeat tests
• Muscle cramps or heart rhythm symptoms
• Alongside kidney and electrolyte results
• Response to diet or supplements

What to ask your doctor

• Does normal blood level rule out deficiency?
• Should I be tested a different way?
• Could a medication be lowering this?
• Do I need to supplement?

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