Causes of Hypokalemia
Hypokalemia, defined as serum potassium less than 3.5 mEq/L, is the most common electrolyte abnormality and can result from decreased intake, increased losses, or transcellular shifts. 1, 2
Major Causes of Hypokalemia
1. Decreased Intake
- Inadequate dietary potassium intake (rarely causes hypokalemia alone) 3
2. Increased Losses
Renal Losses
- Diuretic therapy - most common cause 1, 4
- Loop diuretics (furosemide)
- Thiazide diuretics (chlorothiazide)
- Mineralocorticoid excess
- Primary hyperaldosteronism
- Secondary hyperaldosteronism
- Renal tubular disorders
- High-dose glucocorticoids
- Magnesium deficiency
- Antibiotics (penicillin derivatives, aminoglycosides)
- Renal tubular acidosis
Gastrointestinal Losses
- Vomiting
- Diarrhea
- Nasogastric suction
- Laxative abuse
- Intestinal fistulas
- Short bowel syndrome 1
3. Transcellular Shifts
- Insulin administration
- Beta-adrenergic stimulation
- Alkalosis (metabolic or respiratory)
- Hypokalemic periodic paralysis
- Hypothermia
- Barium poisoning
- Vitamin B12 or folic acid treatment of megaloblastic anemia
Medication-Induced Hypokalemia
- Diuretics (loop and thiazide) 1
- Beta-agonists (albuterol)
- Insulin
- Theophylline
- High-dose penicillins
- Amphotericin B
Clinical Presentation Based on Severity
- Mild (3.0-3.5 mEq/L): Often asymptomatic
- Moderate (2.5-2.9 mEq/L): Muscle weakness, fatigue, constipation
- Severe (<2.5 mEq/L): Cardiac arrhythmias, paralysis, rhabdomyolysis 1, 5
Diagnostic Approach
Measure urinary potassium:
Assess acid-base status:
- Metabolic alkalosis: Suggests vomiting, diuretic use
- Metabolic acidosis: Suggests diarrhea, RTA
Blood pressure measurement:
- Hypertension: Suggests mineralocorticoid excess
- Hypotension: Suggests volume depletion (vomiting, diarrhea)
Common Pitfalls and Caveats
- Hypokalemia often coexists with hypomagnesemia, which must be corrected for successful potassium repletion 1
- Pseudo-hypokalemia can occur with prolonged storage of blood samples
- Patients with heart failure should maintain potassium levels of at least 4 mEq/L 1
- Rapid correction of severe hypokalemia can cause cardiac arrhythmias
- ECG changes (U waves, ST depression, T wave flattening) may indicate severe hypokalemia requiring urgent treatment 1, 5
Special Considerations
- In patients with short bowel syndrome, hypokalemia is often secondary to sodium depletion with secondary hyperaldosteronism 1
- In heart failure patients on diuretics, hypokalemia increases risk of ventricular arrhythmias 1
- Hypokalemia in the setting of chronic kidney disease suggests excessive losses rather than inadequate intake 1
Understanding the underlying cause of hypokalemia is essential for appropriate management and prevention of recurrence, with diuretic therapy being the most common etiology in clinical practice.