Hypokalemia
Hypokalemia is a serum potassium level below 3.5 mEq/L, most often caused by gastrointestinal or renal potassium losses, and it produces weakness, ileus, and arrhythmia risk through altered membrane excitability. Diagnosis rests on the urine potassium-creatinine ratio to separate renal from extrarenal causes, and treatment is intravenous or oral potassium chloride, with concurrent magnesium repletion, dosed to severity and symptoms.
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What this article covers
- Overview
Low serum potassium from transcellular shift or true total-body depletion: defined as a serum potassium <3.5 mEq/L (3.5 mmol/L), divided into disorders of internal balance (potassium moving between…
- Epidemiology
One of the most frequently encountered electrolyte abnormalities in both hospitalized and outpatient settings, driven primarily by diuretic use, gastrointestinal losses, and transcellular shifts.
- Risk factors
Loop and thiazide diuretic use: the most common drug cause, from increased distal delivery and secretion of potassium; loop diuretics also waste calcium and both classes cause hyperuricemia.
- Pathophysiology
Two mechanistic categories: transcellular shift (internal balance) or true total-body depletion (external balance).
- Clinical features
Muscle weakness or frank paralysis is the dominant early symptom, reflecting impaired neuromuscular excitability; severity tracks the degree and rate of fall of serum potassium.
- Differential diagnosis
Pseudohypokalemia: a spurious low reading from delayed sample processing that allows metabolically active leukocytes to take up potassium (classically in leukemia), distinguished by leukocytosis and the absence of expected signs/symptoms.
- Diagnosis
The diagnosis is confirmed by a serum potassium level <3.5 mEq/L.
- Management
First, assess for neuromuscular or cardiac symptoms and check an ECG, since their presence, or a level <2.5 mEq/L, defines the population needing urgent IV repletion rather than oral supplementation.
- Complications
Life-threatening cardiac arrhythmia, including ventricular tachycardia and torsade de pointes, particularly with concurrent hypomagnesemia, QT-prolonging drugs, or structural heart disease.
- Prognosis
Excellent with prompt recognition and correction, particularly for drug-induced or transient shift-related hypokalemia, which resolves once the cause is removed.
- Prevention
Check serum potassium periodically in any patient started on a loop or thiazide diuretic, particularly in the first weeks and after dose increases, and add a potassium-sparing agent or potassium…
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