Test library
Magnesium RBC Test
The Magnesium RBC Test measures magnesium inside red blood cells, which some clinicians use as a longer-term view of magnesium status than a serum measurement provides.
Order Magnesium RBC Test
Order online and visit a local collection site, or choose an at-home kit where available. No referral and no insurance required.
Order Magnesium RBC Test- Typical turnaround
- 1-3 business days
- Starting price
- From $158
- Results
- Confidential, online
Quick answer
The Magnesium RBC Test measures the magnesium content of red blood cells. Because most magnesium in the body sits inside cells, this test is sometimes used when a person has symptoms that suggest low magnesium but a serum magnesium level looks normal. It offers a different window on magnesium status, though interpretation varies between laboratories. Results are read alongside serum magnesium and the overall clinical picture.
What this test measures
Magnesium performs its roles largely inside cells, and red blood cells are easy to sample for an intracellular view. The test measures magnesium concentration within those cells rather than in serum. Because red blood cells live for about three months, the measurement is often described as reflecting a longer window than a serum level, which can fluctuate day to day.
The sample is a standard blood draw collected in a tube appropriate for this assay. Laboratories differ in their methods and reference ranges, so a result should always be compared with the range reported by the performing laboratory. Some providers order the RBC magnesium together with a serum magnesium, calcium, potassium, and kidney markers for a fuller assessment.
The test may be ordered when symptoms such as muscle cramps, fatigue, or palpitations raise concern about magnesium status and serum testing has been inconclusive. It is not a stand-alone diagnostic test, and a qualified healthcare provider should interpret it with the person's history, diet, medicines, and other laboratory results.
- Magnesium in red blood cells (RBC magnesium)
- Serum magnesium when paired
- Calcium when included
- Potassium when included
- Albumin when included
- Creatinine when included
- Estimated glomerular filtration rate (eGFR) when included
Why people order this test
- Assess magnesium status when serum levels look normal but symptoms persist
- Get a longer-term view of magnesium than a single serum result
- Follow up on unexplained muscle or heart-related symptoms
- Check magnesium alongside other minerals and kidney markers
- Support a nutritional or metabolic evaluation with a clinician
How to prepare
No fasting is usually required, but follow the laboratory's instructions for this specialized assay. Tell the collection staff about any magnesium supplements or medications you take, because they can influence the result.
Understanding your results
Results are typically available within one to three business days. Because laboratories use different methods and ranges, the reported reference interval is the basis for comparison. A qualified healthcare provider interprets the value with the person's symptoms and other findings.
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Frequently Asked Questions
How is the RBC magnesium test different from a serum magnesium test?
The serum test measures magnesium in the liquid part of blood, while the RBC test measures magnesium inside red blood cells. The RBC value is often described as reflecting a longer period.
Why would a provider order the RBC test instead of serum magnesium?
It may be used when symptoms suggest low magnesium but serum levels appear normal, or to add a second view of magnesium status.
Is there a standard reference range for RBC magnesium?
Reference ranges differ between laboratories because methods vary. The range printed on your report is the one that applies to that result.
Can I take magnesium before this test?
Tell the collection staff about any supplements you take. Whether to pause them is a decision for the ordering healthcare provider, not the laboratory.
Does the test diagnose a specific condition?
No. It provides information about magnesium status that a qualified healthcare provider interprets with symptoms, diet, medicines, and other test results.
Ready to get tested?
Order online and visit a collection site near you, or choose a mail-in kit. No referral and no insurance required.
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