Magnesium Blood Test
Reviewed
Also called: Mg, Mag, Magnesium-Serum
A magnesium blood test measures the amount of magnesium in a sample of your blood.
Specimen: blood
Why this test may be ordered
- To check magnesium level if your health care provider thinks your levels may not be normal
- To help find the cause of abnormal levels of other minerals such as calcium, potassium, and phosphorus
- To monitor health if you have a condition linked to abnormal magnesium levels (e.g., chronic kidney disease, diabetes, alcohol use disorder, malabsorption syndrome, malnutrition, chronic diarrhea, low potassium/calcium)
- To monitor if you take medicines that can decrease magnesium (diuretics, certain antibiotics, proton pump inhibitors) or increase magnesium (aspirin, magnesium-containing laxatives/antacids, lithium)
- To monitor if you are being treated with magnesium and/or calcium
Preparation and collection
There's usually no preparation for a magnesium blood test. If you're having other blood tests at the same time, you may need to fast (not eat or drink) for several hours before your test. Be sure to tell your provider about any prescription and over-the-counter medicines and/or supplements that you are taking.
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
Understanding results
If the results of your magnesium blood test are abnormal, your provider will use your medical history and the results of other tests to diagnose the cause.
- Low magnesium: In general, low magnesium levels may mean that: You're not getting enough magnesium in your diet. Your body isn't able absorb magnesium, even if you eat the right amount. Your body is getting rid of too much magnesium. Limitation: Many different conditions can affect magnesium levels, so ask your provider to explain what your test results mean. Next step: To get more information about your magnesium levels, your provider may also order a magnesium in urine test or a magnesium red blood cell (RBC) test.
- High magnesium: Higher than normal magnesium levels may mean that: You're getting too much magnesium from dietary supplements, laxatives, antacids, or certain prescription medicines. Your body has a problem getting rid of magnesium. The most common cause is kidney failure. Limitation: It's rare to get too much magnesium from food alone. Next step: Many different conditions can affect magnesium levels, so ask your provider to explain what your test results mean.
- The amount of magnesium in your blood may be normal even though the amount stored in your body is low. Your provider may order a magnesium in urine test or a magnesium red blood cell (RBC) test for more information.
- name
- Magnesium Blood Test
- nextSteps
- Treatment for abnormal magnesium levels will depend on your condition. Your provider will discuss next steps with you.
What to do next
Treatment for abnormal magnesium levels will depend on your condition.
- What do my magnesium blood test results mean in my specific situation?
- Do I need any follow-up tests, such as a magnesium urine test or magnesium RBC test?
- What conditions could be causing my abnormal magnesium level?
- Should I change my diet or any medicines I am taking?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.