The short answer
Red-blood-cell magnesium — a more sensitive measure of your body's true magnesium stores than the standard serum test, measured from a standard blood draw. At TestWell it costs $29.99 plus a $6 lab processing fee, needs no fasting, and results post in 5–9 business days. Physician-authorized with no doctor's visit or insurance needed; draw at Quest or Labcorp.
Hospital Lab
$95
cash pay
Other Labs
$45
+ lab fees
TestWell
$29.99
+ $6 lab processing fee
Magnesium, RBC measures the magnesium held inside your red blood cells rather than in the serum. Because most of the body's magnesium is stored intracellularly, RBC magnesium is considered a more sensitive indicator of long-term magnesium status and can reveal a deficiency even when a standard serum magnesium reads normal. It's often ordered by practitioners investigating fatigue, muscle cramps, poor sleep, anxiety, migraines, or irregular heartbeat when a serum test wasn't conclusive.
Vitamin and nutrient testing identifies deficiencies that can drive fatigue, immune dysfunction, neurological symptoms, and long-term disease risk — and confirms that supplementation is working.
Anyone with restrictive diets (vegan, low-fat, low-carb), malabsorption conditions, fatigue, hair loss, mood changes, or currently supplementing and wanting to verify dosing.
Sample Type
Blood draw
Fasting
Not required
Results In
5–9 business days
Performed At
Quest or Labcorp
1 biomarker tested
Your Magnesium, RBC results will include values for each of the 1 biomarker tested, along with reference ranges. Results are reviewed by a licensed physician before being released to your secure portal.
If any values fall outside the normal range, your report will include guidance on what that may mean and recommended next steps. You'll receive an email notification when your results are ready, typically within 5–9 business days.
Typical reference range layout
Lab reports show where your value sits relative to established reference intervals—your physician interprets this in context for you. Already have results? Analyze them with your AI assistant against our physician-reviewed ranges.
No fasting required.
What can throw off this result
Physician-reviewed “Before your test” pages — what each factor does, for how long, and what to do about it.
TestWell orders the same Magnesium, RBC the labs run for doctors' offices, so you can walk into any of these labs with our requisition — no doctor's visit, a licensed physician authorizes the order, and most patient service centers take walk-ins. The table shows each lab's own test code, the name printed on the requisition, what the lab charges on its own consumer site, and the price through TestWell at that lab (plus one $6 fee per order).
| Lab | Test code | On the requisition | Lab's own site | Through TestWell |
|---|---|---|---|---|
| Quest Diagnostics | test code 623 | “Magnesium, RBC” | not sold direct | $29.99 + $6 |
| Labcorp | test no. 080283 | “Magnesium, RBC” | not sold direct | $29.99 + $6 |
| BioReference (New York & New Jersey) | test code 1383-9 | “Magnesium, RBC” | n/a | $29.99 + $6 |
You choose the lab at checkout; the requisition is written for that lab and arrives by email within minutes. New York and New Jersey orders draw at BioReference. Lab-direct prices are read from the labs' public pages and re-checked regularly.
Where to get it near you: patient service centers by state and city · search by ZIP code
An RBC Magnesium test costs $29.99 at TestWell — $35.99 all-in, since the $6 lab processing fee is charged once per order and there is no draw or physician fee. Hospital outpatient labs typically bill around $95.00 self-pay. With insurance you pay your plan's negotiated rate against your deductible; TestWell's price is fixed before the draw and HSA/FSA-eligible.
| Where you order | Price | One test, all-in | Notes |
|---|---|---|---|
| TestWell (drawn at Quest or Labcorp) | $29.99 | $35.99 | Includes the one $6 lab processing fee, charged once per order |
| TestWell (drawn at BioReference — New York & New Jersey) | $29.99 | $35.99 | New York and New Jersey orders route to BioReference; Quest Health and Labcorp OnDemand don't take self-ordered draws in those states |
| Hospital outpatient lab, self-pay (typical) | $95.00 | $95.00 | Reference figure; hospital charges vary widely by facility and are often higher |
Lab test codes: Quest test code 623 · Labcorp test no. 080283 · BioReference code 1383-9. Competitor prices are read from the linked public pages and re-checked regularly; the labs' sites may add taxes or change prices without notice.
Compare more: Quest Diagnostics price list · Labcorp price list · Quest vs Labcorp · Lab test price checker
Most Magnesium, RBC results are available in 5–9 business days after your specimen arrives at the lab. You'll get an email the moment results are ready, with everything viewable in your TestWell portal.
Blood draw. A standard venous blood draw, collected at any Quest, Labcorp or BioReference patient service center — walk in with the requisition we email you, no appointment needed at most locations.
On TestWell, the Magnesium, RBC is $29.99. Quest Direct lists comparable tests at $45. Walk-in hospital labs typically bill $95 or more without insurance. Insurance is not required — pay one all-in price.
The Magnesium, RBC is available at Quest and Labcorp patient service centers nationwide. Order online at TestWell, pick your preferred lab, and we'll generate a digital requisition for the location closest to you.
No, fasting is not required for an RBC Magnesium test — you can eat normally and book any time of day.
Common medications and keto and high-protein diets can change an RBC Magnesium test result without anything being wrong. Common medications can lower Magnesium, RBC — check magnesium and B12 on long-term PPIs. Keto and high-protein diets can lower Magnesium, RBC — hydrate and mention the diet if a metabolic panel is drawn in the transition. Each is explained on our physician-reviewed "Before your test" pages; when one applies, remove it and retest.
The CPT code for an RBC Magnesium test is 83735. You can order it from TestWell for $29.99 — no doctor's visit or insurance required, with results in 5–9 business days.
The RBC Magnesium test is Quest Diagnostics test code 623, Labcorp test number 080283, BioReference code 1383-9 (CPT 83735). TestWell orders it under those codes for $29.99 at Quest, Labcorp or BioReference — no doctor's visit or insurance required, results in 5–9 business days. Codes verified against the labs' catalogs in 2026.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
TestWell Price
$29.99
+ $6 lab processing fee at checkout
No insurance needed · HIPAA compliant
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Magnesium, RBC
$29.99