Normal Range for Potassium in Healthy Adults
The normal range for serum potassium in healthy adults is 3.5-5.0 mEq/L (or mmol/L), though optimal levels for cardiovascular health appear to be 4.0-5.0 mEq/L. 1, 2
Standard Laboratory Reference Range
- The conventional normal range is 3.5-5.0 mEq/L, with hypokalemia defined as levels below 3.5 mEq/L and hyperkalemia as levels above 5.0 mEq/L 2
- Only 2% of total body potassium exists in the extracellular fluid (where serum measurements occur), meaning small serum changes reflect substantial total body deficits 1, 3
Optimal Range for Cardiovascular Health
For patients with cardiac disease, heart failure, or other high-risk conditions, maintaining potassium between 4.0-5.0 mEq/L minimizes mortality risk. 1, 4
- Multiple studies demonstrate a U-shaped mortality curve, where both low and high potassium levels increase death risk, with the nadir occurring at 4.0-5.0 mEq/L 1
- Patients with heart failure, chronic kidney disease, or diabetes show significantly greater mortality risk when potassium levels fall outside the 4.0-5.0 mEq/L range 1
- Even "high-normal" levels (5.0-5.5 mEq/L) may be associated with better outcomes in some heart failure populations, though this remains controversial 1, 5
Context-Dependent Considerations
The acceptable potassium range narrows in specific clinical contexts:
- Cardiac patients on digoxin: Maintain 4.0-5.0 mEq/L strictly, as hypokalemia potentiates digitalis toxicity 4, 6
- Post-myocardial infarction patients on loop diuretics: Optimal range appears to be 3.9-4.5 mEq/L 1
- Hypertensive patients: Levels outside 4.1-4.7 mEq/L associated with higher mortality 1
- Patients with CKD stage 4-5: Broader tolerance toward higher levels (3.3-5.5 mEq/L optimal) due to adaptive mechanisms 1
Clinical Symptoms by Severity
- 3.0-3.5 mEq/L (mild hypokalemia): Often asymptomatic, though muscle weakness and fatigue may occur 3, 2
- Below 2.7 mEq/L: Clinical problems typically manifest, including significant muscle weakness 6
- ≤2.5 mEq/L (severe hypokalemia): Risk of muscle necrosis, paralysis, cardiac arrhythmias, and respiratory impairment 3, 2
- Above 7.0 mEq/L (severe hyperkalemia): Life-threatening cardiac conduction disturbances 6
Dietary Recommendations
The World Health Organization recommends a potassium intake of at least 3,510 mg per day (90 mmol/day) for optimal cardiovascular health 1, 2