Potassium, RBC
Potassium inside red blood cells, a window into intracellular stores that serum levels can miss.
Consider this test if:
- Persistent fatigue, muscle weakness, or cramping with normal serum potassium
- Investigating low magnesium, which commonly drives intracellular potassium loss
- Palpitations or irregular heartbeat being worked up alongside electrolytes
- Tracking cellular electrolyte status over time rather than a single serum reading
- HSA/FSA eligible
- Results delivered to your dashboard · Reviewed by a real clinician
- Drawn at a CLIA/CAP-accredited lab near you ·
Pre-test considerations
No fasting required. Sample handling matters: hemolysis and delays before processing can distort potassium results, so the draw should be transported promptly per lab instructions. Note any potassium or magnesium supplements and diuretics, since they affect levels.
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What this test is for
Potassium is the main intracellular cation, essential for nerve signaling, muscle contraction, and steady heart rhythm. This test measures potassium inside red blood cells rather than in serum, so it reflects the body's intracellular stores, where about 98% of total-body potassium sits. RBC potassium can stay informative when serum potassium reads normal, since serum is tightly regulated and represents only the small fraction circulating outside cells. Low intracellular potassium is often investigated alongside fatigue, muscle weakness, cramping, palpitations, and magnesium status, since magnesium depletion drives potassium loss.
For most routine questions, the standard serum or plasma potassium test is the right marker and the one used to assess acute high or low potassium. RBC potassium is the specialized form, used when you want a longer-term view of cellular potassium status rather than the moment-to-moment serum level.
What to expect
- 1 Book instantly
Click, book, done. Choose a convenient lab location near you. Transparent, up-front pricing.
- 2 Quick lab visit
Testing to fit your busy schedule, usually 15 minutes or less. Walk-in and appointments available.
- 3 Fast, dashboard-delivered results
Your results post straight to your dashboard as soon as the lab completes them.
- 4 Expert guidance
Included with Mito membership. A clinician reviews your results and your personalized action plan follows, with clear next steps.
Everything your health needs,
in one membership
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Every test at our cost
Members pay our cost on every test, with lab fees passed straight through. The full receipt is itemized, never padded.
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Continuous tracking, all in one place
Upload past labs and watch your trends over time. Every marker and visit lives in one longitudinal record, so all your care stays together.
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Year-round clinician support
Text anytime and get clinician-reviewed answers. When you want to go deeper, 1:1 consultations are available at affordable rates.
All for $9/month
Order any test or consult without joining. For $9/month, members unlock member prices, trend tracking, and year-round clinician guidance.
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Frequently asked questions
View all FAQsHow does pricing work?
Every test shows the member price next to the standard non-member price, so you can see what membership saves you. The member price is our cost — covering the lab and what it takes to run the service — never a profit on the test itself; Mito makes its money on the $9 membership, not on marking up your tests. Membership is $9/mo, and you still pay the lab’s order fee. Prices are itemized before you pay, with no hidden fees.
Where do I get tested?
Choose a partner lab (Quest, Labcorp, or BioReference) at checkout. If your cart spans multiple tests, we consolidate the whole order onto a single lab so you only make one visit.
Is this eligible for HSA/FSA?
Yes. This test is HSA/FSA eligible, and you can pay with your HSA/FSA card at checkout.
When will I get my results?
Your results post to your dashboard once your lab completes them, then a clinician reviews them and your full analysis and personalized action plan (with clear next steps) follow. Turnaround varies by test: specialty assays and at-home kits take longer, and each test shows its expected turnaround before you buy.
Do I need a doctor’s order?
No. Mito provides the lab order for you, so you can book and get tested without a separate doctor visit.
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