Nutrients
Magnesium (Mg)
Serum magnesium, RBC magnesium
Included in Baseline and Complete. Complete adds RBC magnesium.
Compare membershipsMeasuring magnesium is trickier than it sounds.
Magnesium helps your muscles, nerves, heart rhythm, blood sugar control, and bones work properly. Most of it sits in your bones and other tissues, with only a small fraction in your blood.
Serum and red blood cell magnesium tell different stories.
Serum magnesium measures the magnesium in the liquid part of your blood. It's the standard clinical test, though your kidneys keep it in a tight range, so it can look typical even when tissue stores are lower. RBC magnesium measures the magnesium inside red blood cells. Methods and reference ranges aren't standardized between labs, and evidence on how well it reflects body stores is limited.
The NIH notes that no single method is considered satisfactory. Diuretics, acid-reducing medicines, poorly controlled diabetes, alcohol use, and digestive conditions can all lower magnesium.
A typical serum magnesium doesn't always mean full stores.
Questions
Why measure both serum and RBC magnesium?
Each has limits. Serum magnesium is the standard test and is useful for finding clearly low or high levels. RBC magnesium looks inside cells, but it's less established, so it adds context. A clinician reads both with your diet, medications, and symptoms.
Can magnesium be too high?
It's uncommon. High blood magnesium happens mostly in people with kidney failure, and magnesium-containing laxatives or antacids can also raise it. If your result is high, your clinician will look at your kidney function.