Potassium
K· also: K+, Potassium, Serum Potassium
Clinical Overview
Potassium is the primary intracellular cation and is essential for maintaining the resting membrane potential of cells, particularly in cardiac muscle and nerves. Even small deviations from the normal range can cause life-threatening cardiac arrhythmias. Potassium is tightly regulated by the kidneys and aldosterone.
Why This Test Matters
Potassium disorders are among the most dangerous electrolyte emergencies. Both hypokalemia and hyperkalemia can cause fatal cardiac arrhythmias — hyperkalemia causes peaked T waves, widened QRS, and ventricular fibrillation; hypokalemia causes U waves, prolonged QT, and torsades de pointes. Potassium must always be interpreted alongside an ECG in symptomatic patients and at critical values.
Reference RangesWHO/IFCC standards
| Reference Range | Unit | Notes |
|---|---|---|
| 3.5 – 5 | mEq/L | — |
Also reported in: mmol/L.
Critical (Panic) Values
Critical Low: < 2.5 mEq/L. Critical High: > 6.5 mEq/L. Values outside these limits require immediate clinical attention.
What Causes Abnormal Results?
High K Causes
- Kidney failure (most common — reduced excretion)
- ACE inhibitors and ARBs (reduce aldosterone effect)
- Potassium-sparing diuretics (spironolactone, amiloride)
- Addison's disease (adrenal insufficiency)
- Metabolic acidosis (potassium shifts out of cells)
- Rhabdomyolysis (cell rupture releases intracellular potassium)
- Pseudohyperkalemia from hemolyzed blood sample (very common artifact)
Low K Causes
- Diuretics (thiazides, loop diuretics — most common cause)
- Vomiting and nasogastric suction
- Diarrhea and laxative abuse
- Hyperaldosteronism (primary or secondary)
- Hypomagnesemia (potassium wasting accompanies magnesium deficiency)
- Refeeding syndrome
- Insulin therapy (drives potassium into cells)
- Alkalosis (potassium shifts into cells)
Signs & Symptoms to Watch For
How to Prepare for This Test
No special preparation. Potassium can be falsely elevated by hemolysis (most common lab artifact) — the specimen should be processed promptly without excessive shaking or delay.
Factors That Can Affect Results
- Hemolysis (most common cause of falsely high potassium — red cells contain 20–50× more potassium than plasma)
- Prolonged tourniquet with fist clenching (localizes potassium from muscle, raises local potassium)
- Cold temperature (potassium leaks from cells in cold storage)
- Thrombocytosis or leukocytosis (platelets and white cells release potassium on clotting)
- Insulin and beta-2 agonists (lower serum potassium by driving it into cells)
Related Topics
Frequently Asked Questions
Why does a hemolyzed sample cause falsely high potassium?
Potassium is predominantly intracellular. Red blood cells contain approximately 105 mEq/L of potassium, versus only 3.5–5 mEq/L in plasma. When red cells rupture (hemolysis) during blood collection, storage, or processing, intracellular potassium is released into the plasma, dramatically raising the measured potassium level. This pseudohyperkalemia is the most common cause of an unexpectedly high potassium result — always repeat the test with a non-hemolyzed sample before treating.
How is severe hyperkalemia treated?
Treatment of hyperkalemia above 6.5 mEq/L with ECG changes is a medical emergency. Steps include: (1) Calcium gluconate IV — immediately stabilizes cardiac membranes; (2) Insulin + glucose IV — drives potassium into cells within 15–30 minutes; (3) Sodium bicarbonate — shifts potassium into cells in acidotic patients; (4) Salbutamol (albuterol) nebulization — lowers potassium within 30 minutes; (5) Kayexalate, patiromer, or sodium zirconium cyclosilicate (ZS-9) — remove potassium from the body over hours; (6) Dialysis — for refractory cases or kidney failure.