Potassium, RBC
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Blood Test for Muscle Weakness and Fatigue
Potassium, RBC
- Measures potassium inside red blood cells
- Assesses electrolyte balance
- Useful in diagnosing potassium deficiencies
$322
Example results
First results as soon as overnight*
90 day happiness guarantee
We stand behind our service
Prescription & fees included
Go directly to the lab, no extra fees
Easy to understand results
With friendly doctor's notes & guidance
Fast & convenient
Lab visit as quick as 10 mins in & out
90 day happiness guarantee
We stand behind our service
Prescription & fees included
Go directly to the lab, no extra fees
Easy to understand results
With friendly doctor's notes & guidance
Fast & convenient
Lab visit as quick as 10 mins in & out
What's this test for?
This test is ideal if you're experiencing unexplained muscle weakness, fatigue, cramping, or irregular heartbeat that might be related to potassium imbalances. It measures potassium levels inside your red blood cells, which gives a more accurate picture of your body's true potassium stores compared to standard blood tests. Many people use this test when they suspect nutritional deficiencies or want to understand why they're experiencing ongoing fatigue or muscle-related symptoms.
What's included in this test?
This test measures potassium, RBC, which assesses the concentration of potassium inside your red blood cells rather than in your blood plasma. This intracellular measurement is important because most of your body's potassium is stored inside cells, making RBC potassium a more reliable indicator of true potassium status than standard serum tests. This is especially useful for detecting hidden deficiencies that can cause fatigue, muscle problems, and electrolyte imbalances that don't show up on regular blood work.
What happens after I get my results?
You'll receive detailed doctor notes in simple language explaining what your red blood cell potassium levels mean for your energy, muscle function, and overall health. These notes include personalized recommendations like dietary changes to increase potassium intake, supplement suggestions if appropriate, or whether you should follow up with your doctor about underlying causes. You'll also get the standard lab report and can track your potassium levels over time using our trends feature to see how dietary changes are working.
Who should consider getting this test?
This test is particularly useful for people experiencing chronic fatigue, muscle weakness, or cramping that hasn't been explained by standard blood work. It's also valuable for individuals with digestive issues, those taking diuretics or other medications that affect electrolytes, athletes with performance issues, or anyone with a history of low potassium on regular tests who wants a more accurate assessment of their cellular potassium stores.
What symptoms indicate I may need this test?
Common symptoms of low intracellular potassium include persistent muscle weakness, frequent cramping or muscle twitches, unexplained fatigue that doesn't improve with rest, irregular heartbeat or palpitations, constipation, and tingling or numbness in extremities. If you've had normal potassium results on standard blood tests but still experience these symptoms, checking RBC potassium can reveal hidden deficiencies.
How can I naturally support my potassium levels?
Increase your intake of potassium-rich foods like bananas, sweet potatoes, spinach, avocados, beans, yogurt, salmon, and oranges. Aim for the recommended 2,600-3,400 mg of potassium daily through whole foods rather than supplements, which can be dangerous without medical supervision. Reduce processed foods high in sodium, stay well-hydrated, and if you exercise heavily or sweat a lot, ensure you're replacing lost electrolytes through balanced meals.
What is intracellular potassium and why does it matter?
Intracellular potassium is the potassium stored inside your cells, where about 98% of your body's potassium actually lives. It's crucial for muscle contraction, nerve signaling, heart rhythm, and cellular energy production. Unlike standard potassium tests that measure blood serum levels, RBC potassium testing reveals what's happening inside your cells, providing a more accurate picture of your true potassium status and helping identify deficiencies that other tests might miss.
What does low RBC potassium mean?
Low RBC potassium indicates that your cells aren't getting enough potassium, even if your blood serum levels appear normal. This can lead to muscle weakness, fatigue, cramping, irregular heartbeat, and reduced physical performance. Low intracellular potassium may result from poor dietary intake, digestive absorption issues, certain medications like diuretics, chronic stress, or conditions that cause potassium loss.
What causes low intracellular potassium?
Low RBC potassium can be caused by inadequate dietary intake of potassium-rich foods, digestive disorders that impair nutrient absorption, prolonged use of diuretics or other medications, chronic diarrhea or vomiting, excessive sweating from intense exercise, high sodium intake, chronic stress, or conditions like kidney disease. Sometimes magnesium deficiency also prevents proper potassium absorption into cells.
How often should I retest my RBC potassium?
If you're actively working to improve low potassium levels through diet or supplements, retesting in 8-12 weeks allows time to see meaningful changes. If your levels are normal and you're just monitoring for maintenance, annual testing is usually sufficient. However, if you start new medications that affect electrolytes or experience returning symptoms, earlier retesting may be appropriate to ensure your cellular potassium remains optimal.
How’s this work?
Long story short:
- In the test options, use the filters or search box to narrow your choices and find the test you want.
- If you need a hand navigating through options, text our super friendly support team at 754-799-7833, and we'll provide tailored suggestions to help you find the ideal test.
- Once your order is placed, we’ll create your doctor’s lab order remotely, without any need for you to make a trip to a doctor in person or to talk to the doctor. Expect to receive your doctor’s lab order right in your inbox. It will also be in your patient portal if you need to find it later. We’ll also include instructions regarding fasting and other requirements for your test. Your patient portal will be auto-created hassle-free during checkout.
- If this is your first time ordering, you'll be prompted to create a password for instant login access to your patient portal. It's a quick way to conveniently access your orders and results whenever you want.
- When you’re ready, visit one of our 4,000 locations. Just bring your ID – no printing or faxing of your lab order is needed, as your order and details will already be in the lab system.
- Note that most lab locations don’t accept walk-ins, so it’s best to book an appointment in advance. Don’t worry – we’ll provide detailed instructions along the way.
- You’ll get your results via email & SMS and dive into understanding your body better. Yup, that easy! If you have any questions, please text us at 754-799-7833 or email [email protected] and we'll gladly help you.
How do I know which test to get?
Just text or call us at 754-799-7833, email us at [email protected], and we'll gladly help you. We've got your back and reply quickly.
Is it possible to make changes to my lab order if I made a mistake with the name, date of birth, or any other details?
Just reach out to us via text at 754-799-7833 or shoot us an email at [email protected]. Remember to include your order number and let us know the correct information you’d like to update. Our awesome team will jump right in and make sure everything is sorted out and accurate for you.
There are no changes necessary if your address is wrong on the requisition though. We don’t mail anything out.
Our lab requires an address to be listed to generate an order.
Do you accept health insurance?
Our services are strictly self-pay and cannot be submitted to your health insurance provider except for Health Savings Accounts or Flexible Savings Accounts.
This policy applies to all insurance companies, including federal health insurance programs like Medicare.
If you have any questions, please text us at 754-799-7833 or email [email protected].
Can I cancel my order?
We get it – sometimes your needs change.
As long as your samples haven’t been collected yet, we’re happy to help you cancel your order.
If you have any further questions, please text us at 754-799-7833 or email [email protected].
You can read more about our cancellation policy here.
How can I find a lab location near me?
Before you proceed with your order, feel free to browse through all our lab locations here. This will give you the peace of mind of knowing that there's a lab nearby your home, office or your favorite gym.
If you have any questions, please text us at 754-799-7833 or email [email protected] and we'll gladly help you.
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Demo results
Potassium, RBC
82 mmol/L
Demo results
Low
Optimal 85 - 105
High
82 mmol/L
What this means
Your red blood cell potassium level is slightly below the optimal range, which may explain symptoms like muscle weakness, fatigue, or cramping. While your regular blood potassium might test normal, this intracellular measurement reveals your cells aren't getting enough potassium for optimal function.
Recommended actions
Increase potassium-rich foods like bananas, sweet potatoes, spinach, avocados, and beans
Ensure adequate magnesium intake, which helps cells absorb potassium properly
Stay well-hydrated and reduce high-sodium processed foods
Retest in 8-12 weeks after making dietary improvements
* Regular blood test results (e.g., CBC) typically start arriving the next business day after sample collection. More complex tests, such as hormone panels, may take up to 10–15 business days due to their complexity.
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Blood Test for Muscle Weakness and Fatigue
- Measures potassium inside red blood cells
- Assesses electrolyte balance
- Useful in diagnosing potassium deficiencies
$322
Example results
1,000,000+ blood tests later, here's what our customers say
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