Lab test
Magnesium RBC Test – Deficiency Testing
Below is a plain-language overview of the magnesium rbc test – deficiency testing. A magnesium RBC test measures the amount of magnesium inside red blood cells, which some clinicians consider a more accurate reflection of body magnesium status than a serum magnesium test.
Lab requirements in Magnesium RBC Test – Deficiency Testing
Here is what you need before ordering and completing the Magnesium RBC Test – Deficiency Testing. Review each item and confirm the details with the collection lab.
- Physician's order
- Included. A physician's order is required for lab testing and is provided for you by our partner's physicians — no referral from your own doctor is needed.
- Fasting
- Fasting is required for this test — follow the collection lab's instructions.
- Preparation
- Preparation instructions can vary, so follow the specific directions provided by the collection laboratory. This may include fasting or avoiding certain supplements before the test.
- Sample & visit
- A blood and/or urine sample is collected; the visit usually takes about 10 minutes.
- Identification
- Bring the lab requisition form from your account. The collection lab may also ask for a government-issued photo ID.
- Turnaround
- 1-3 business days
- Availability
- Our partner lab does not serve ND, RI, NY, NJ, MD or HI. Confirm availability for your location with the collection lab.
Before you go
- Order your test before visiting a lab, then use the requisition form in your account.
- Print the requisition form, or fax it to the lab directly from your account.
- No scheduling is needed — visit the collection lab during its normal business hours.
- A blood and/or urine sample is collected; the visit usually takes about 10 minutes.
- Bring a government-issued photo ID in case the lab requests it.
- Results are posted to your secure account within 1–3 business days.
Requirements are summarized from our partner lab's published policies. Preparation and availability can change — confirm current instructions with the collection lab before your visit.
What this test is
This test evaluates the magnesium content within red blood cells rather than in the liquid portion of blood. Because most magnesium is stored inside cells, this test may provide a better picture of overall magnesium levels. It is sometimes used when a standard serum magnesium test is normal but a deficiency is still suspected.
What it measures
- Magnesium (RBC) — Reflects the amount of magnesium stored inside red blood cells
What the test involves
A healthcare professional collects a small sample of blood, usually from a vein in your arm, using a standard blood draw. The sample is then sent to a laboratory for analysis.
Why it is often ordered
A clinician may order this test to assess magnesium status when symptoms such as muscle cramps, weakness, or irregular heartbeat suggest a possible deficiency. It can also be used to monitor conditions or treatments that affect magnesium levels.
Preparation
Preparation instructions can vary, so follow the specific directions provided by the collection laboratory. This may include fasting or avoiding certain supplements before the test.
How results are reported
Results are typically reported as a number that is compared to a reference range established by the testing laboratory. Reference ranges can differ between laboratories, so your results should be interpreted in the context of the lab's own range.
Before you go
- Whether fasting is required before the test
- Any medications or supplements that might affect results
- The specific reference range used by the testing laboratory
FAQ
Frequently asked questions
How is a magnesium RBC test different from a serum magnesium test?
A serum magnesium test measures magnesium in the liquid part of blood, while an RBC magnesium test measures magnesium inside red blood cells. Because most magnesium is stored inside cells, the RBC test may give a more accurate picture of overall magnesium status.
Do I need to fast for this test?
Fasting requirements can vary depending on the laboratory and your healthcare provider's instructions. It is best to check with the collection lab before your appointment to know whether you need to fast.
What can affect my magnesium RBC test results?
Recent intake of magnesium supplements, certain medications, and some health conditions can influence results. Always inform your healthcare provider about any supplements or medications you are taking.
How long does it take to get results?
Turnaround time is typically a few business days, but it can vary by laboratory. Your healthcare provider will discuss the results with you once they are available.
Related
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