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.
- Specimen
- Red blood cells
- Measures
- Substance concentration
What you'll learn
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Insights that connect the dots. A clinician reads your whole picture, not one result in isolation, connecting family history, past results, and lifestyle into clear next steps.
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Your personalized action plan. Nutrition, supplements, and training in one clinician-reviewed protocol, updated as your results change.
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Track your trends. Upload results from any lab and see each biomarker trend over time, so you know what is working.
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Never miss a recheck. Mito tells you what is worth retesting and when, then reminds you so nothing slips.
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. It is never a profit on the test itself. Mito makes its money on the $9 membership, not on marking up your tests. Membership is $9 per month, and any applicable lab order or draw fee is itemized before you pay.
Where do I get tested?
Choose an available partner lab at checkout. If your cart contains multiple blood tests, Mito helps consolidate the eligible tests at one lab when possible. At-home kits and scans follow the collection or appointment process shown on their product page.
Is this eligible for HSA/FSA?
Yes. Eligible tests can be paid for with an HSA or FSA card at checkout.
When will I get my results?
Your results appear in your Mito dashboard after the laboratory completes processing. A clinician then reviews them before your analysis and personalized action plan are finalized. Timing varies by test, and specialty assays and at-home kits may take longer.
Do I need a physician's order?
No. Mito provides the laboratory order when one is required, so you do not need to arrange a separate physician visit before purchasing.
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