Magnesium

What it is

Magnesium is a mineral involved in muscle, nerve, and enzyme function, but only around 1% of your body's magnesium is in the bloodstream — the rest sits in bone and inside cells. That makes serum magnesium a genuinely poor reflection of total body magnesium: the body works hard to hold the blood level steady, so it can look perfectly normal across a wide range of underlying states, which is a well-recognized limitation of this test rather than a quirk of your result. Levels can also be affected by kidney function and by a number of common medications, so it's read in the context of your overall picture rather than as a standalone verdict.

Typical range

Reference ranges vary between laboratories, and what is normal for you depends on your own history. Your own lab’s range is the one printed on your report.

Worth asking your clinician

• Given that blood magnesium only reflects a small fraction of total body magnesium, how much does this result actually tell us about me?
• Could my kidney function or any medication I take be influencing this number?
• Are there symptoms or findings that would make you want to look at magnesium more closely in my case?