RBC magnesium measures magnesium inside red blood cells, reflecting tissue stores more accurately than serum magnesium. Since only about 1% of body magnesium is in the blood at any time, serum testing often misses functional deficiency that RBC testing reveals.
Magnesium is involved in over 300 enzymatic reactions, including energy production, muscle function, nerve signaling, cardiovascular regulation, and sleep. Deficiency is widespread due to depleted soil magnesium, processed foods, and caffeine/alcohol effects on magnesium excretion. Symptoms include muscle cramps, fatigue, poor sleep, anxiety, and cardiovascular irregularities. RBC magnesium is the preferred assessment marker because serum magnesium is tightly regulated and stays "normal" until deficiency is severe.
Optimal Magnesium RBC: 5.5-6.5 mg/dL.
Typically re-tested every 12 weeks.