Magnesium RBC Test
Below is a plain-language overview of the magnesium rbc test. The Magnesium RBC Test measures the amount of magnesium inside red blood cells. It is often ordered when a standard serum magnesium test is normal but a person still has symptoms or conditions linked to low magnesium, such as muscle cramps, weakness, or irregular heartbeat.
- Sample type
- blood
- Category
- Vitamin & Mineral
- Turnaround
- 1-3 business days
- Price
- $158
- Referral
- Not required
The Magnesium RBC Test measures the amount of magnesium inside red blood cells. It is often ordered when a standard serum magnesium test is normal but a person still has symptoms or conditions linked to low magnesium, such as muscle cramps, weakness, or irregular heartbeat.
What it measures
- Magnesium (RBC) — The concentration of magnesium inside red blood cells, which reflects body stores better than a serum test.
- Hemoglobin — A protein in red blood cells that carries oxygen; measured to help interpret the magnesium result.
- Hematocrit — The percentage of blood made up of red blood cells; used to check for anemia or other blood conditions.
Who it is for
This test is typically ordered by a doctor for people with symptoms of magnesium deficiency, such as muscle twitching, fatigue, or abnormal heart rhythms, or for those with conditions that affect magnesium levels, like kidney disease or diabetes.
Preparation
No fasting is required for this test. You can eat and drink normally before your blood draw, but tell your doctor about any medications or supplements you take, as some can affect magnesium levels.
Results and what they mean
Results are reported as a number for magnesium in red blood cells, along with a reference range. Your doctor will interpret the result in the context of your symptoms, other tests, and medical history. This information is not medical advice; always discuss your results with a qualified healthcare professional.
How to order this test
- Choose the test and place a confidential order online.
- Select a certified collection site and pick a time that suits you.
- Have your specimen collected — most draws take only a few minutes.
- Review results in a secure portal, typically within 1–3 days.
Preparation, hours, and pricing vary by site; confirm details directly with the lab before your visit.
Availability by state
Direct-access online ordering for the magnesium rbc test is available in most states. It is currently unavailable in 6 states:
Everywhere else you can order confidentially and collect your sample at a certified site. Browse by state →
Frequently asked questions
How is this test different from a regular magnesium blood test?
A regular serum magnesium test measures magnesium in the liquid part of blood, which can be normal even when body stores are low. The RBC test measures magnesium inside red blood cells, giving a better picture of long-term magnesium status.
Do I need to fast for this test?
No, fasting is not required. You can eat and drink as usual before the blood draw.
What can affect my results?
Certain medications, supplements, and health conditions can affect magnesium levels. Always inform your doctor about what you are taking.
How soon will I get my results?
Results are typically available within 1 to 3 business days. Your doctor will discuss what the results mean for you.