Potassium is an essential mineral and electrolyte that your body needs to function properly. It carries a small electrical charge that activates various cell and nerve functions.
Its most critical job is helping your muscles contract, including the most important muscle in your body: your heart. Keeping potassium levels within a very tight, narrow range is vital for maintaining a normal heart rhythm.
Typical Potassium reference ranges (mmol/L or mEq/L)
| Adults | 3.5 – 5.1 | Ranges are very tight and strictly maintained |
|---|---|---|
| Critical Low | < 2.5 | Requires immediate medical attention |
| Critical High | > 6.0 | Requires immediate medical attention |
Potassium levels are so tightly regulated that even small deviations outside the normal range can be significant.
What low potassium (Hypokalemia) means
A low potassium level is called hypokalemia. Mildly low levels might not cause any symptoms, but as it drops lower, you may experience muscle weakness, cramping, fatigue, and constipation. Severe hypokalemia can cause dangerous heart rhythm abnormalities (arrhythmias).
The most common cause of low potassium is not a lack of potassium in your diet, but rather losing too much of it. This often happens due to prescription diuretics (water pills) used to treat high blood pressure, or from severe vomiting and diarrhea.
What high potassium (Hyperkalemia) means
A high potassium level is called hyperkalemia. Like low potassium, it is particularly dangerous because it can disrupt the electrical signals in your heart. In severe cases, it can lead to cardiac arrest.
Because your kidneys are responsible for filtering out excess potassium, the most common cause of high potassium is chronic kidney disease. Certain blood pressure medications (like ACE inhibitors and ARBs) and potassium-sparing diuretics can also cause levels to rise. Sometimes, a high potassium result is actually a 'false high' caused by red blood cells breaking open during the blood draw (hemolysis) and spilling their potassium into the sample.
When to actually worry — and when not to
- Any result marked 'critical' (usually below 2.5 or above 6.0) requires immediate medical attention, often in an emergency room, due to the risk of heart arrhythmias.
- If you have a flagged potassium result and experience palpitations, a racing heart, skipped beats, or severe muscle weakness, seek urgent care.
- If you are taking blood pressure medications or diuretics and your potassium is consistently borderline or flagged, discuss adjusting your medication with your doctor.
Common questions
Can I just eat more bananas to fix low potassium?
If your potassium is only slightly low due to diet, eating potassium-rich foods (bananas, potatoes, spinach, avocados) can help. However, if it's low because of a medication or illness, diet alone usually isn't enough, and your doctor may prescribe a specific potassium supplement.
What is a 'hemolyzed' sample?
Potassium is highly concentrated inside your red blood cells. If the blood cells break open (hemolyze) during the blood draw or while being transported to the lab, that potassium spills into the serum. This makes the lab result look falsely high, even though the actual potassium level in your body is normal. If your doctor suspects this, they will simply order a repeat test.
One value never tells the whole story.
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Upload your reportMedical disclaimer: This article is for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Reference ranges vary between laboratories — always compare your result to the range on your own report, and consult a qualified healthcare professional about your results and any symptoms.