What causes hypokalemia (low potassium levels)?

Common Causes of Hypokalemia (Low Potassium)

Hypokalemia, defined as serum potassium below 3.5 mEq/L, is most commonly caused by diuretic use, gastrointestinal losses, and renal potassium wasting, with severity classified as mild (3.0-3.5 mEq/L), moderate (2.5-2.9 mEq/L), or severe (<2.5 mEq/L). 1

Major Etiologies of Hypokalemia

1. Excessive Potassium Loss

Renal Losses

• Diuretic therapy - Most common cause, particularly loop diuretics and thiazides 2
• Medications - Caffeine, certain antibiotics 1
• Renal tubular disorders - Especially in premature infants with immature tubular function 1
• Mineralocorticoid excess - Primary hyperaldosteronism, Cushing's syndrome 3
• Magnesium deficiency - Impairs potassium conservation 1

Gastrointestinal Losses

• Vomiting and diarrhea - Common causes of potassium depletion 3
• Nasogastric suction - Prolonged use leads to significant potassium loss 3
• Intestinal fistulas - Continuous fluid losses containing potassium 3
• Laxative abuse - Chronic use causes potassium wasting 2

2. Transcellular Shifts (Normal Total Body Potassium)

• Insulin administration - Drives potassium into cells 2
• Beta-adrenergic stimulation - Stress, epinephrine, beta-agonist medications 2
• Alkalosis - Each 0.1 increase in pH can lower serum potassium by 0.4 mEq/L 4
• Refeeding syndrome - Rapid provision of nutrition after starvation 1
• Hypothermia - Causes intracellular shift of potassium 2

3. Inadequate Intake

• Rarely causes hypokalemia alone - Kidneys can reduce excretion to <15 mmol/day 5
• Contributes when combined with other causes - Particularly in malnourished patients 6

Diagnostic Approach

Initial Assessment

1. Spot urine potassium and creatinine - More practical than 24-hour collection 5

   • Urinary K+ <20 mEq/L suggests extrarenal loss
   • Urinary K+ >20 mEq/L suggests renal potassium wasting

2. Acid-base status evaluation - Critical for determining etiology 5

   • Metabolic alkalosis often accompanies diuretic-induced or vomiting-related hypokalemia
   • Metabolic acidosis with hypokalemia suggests renal tubular acidosis

3. Blood pressure measurement - Helps identify mineralocorticoid excess 5

Clinical Manifestations

Cardiac Effects

• ECG changes - Flattened T waves, ST-segment depression, prominent U waves 1
• Arrhythmias - First or second-degree AV block, atrial fibrillation 1
• Ventricular arrhythmias - PVCs, ventricular tachycardia, torsades de pointes 1
• Increased risk of sudden cardiac death - Especially in patients with heart disease 1

Neuromuscular Effects

• Muscle weakness - May progress to paralysis in severe cases 2
• Rhabdomyolysis - In profound or rapid potassium depletion 2
• Respiratory muscle weakness - Can lead to respiratory failure 3

Other Systems

• Renal effects - Impaired concentrating ability, increased ammonia production 3
• Gastrointestinal effects - Ileus, constipation 3
• Metabolic effects - Glucose intolerance 6

Treatment Considerations

Oral Replacement

• Preferred route when no urgent indications exist 6
• Typical dosing - 40-100 mEq/day for treatment of depletion 4
• Prevention dosing - Approximately 20 mEq/day 4
• Administration - With meals and full glass of water to prevent GI irritation 4
• Divided dosing - No more than 20 mEq in a single dose 4

Intravenous Replacement

• Reserved for severe cases - Symptomatic patients, ECG changes, or inability to take oral supplements 6
• Maximum rate - 10-20 mEq/hour (peripheral IV) or up to 40 mEq/hour (central line with cardiac monitoring) 2

Addressing Underlying Causes

• Potassium-sparing diuretics - Consider for diuretic-induced hypokalemia 6
• Magnesium replacement - Often necessary to correct refractory hypokalemia 1
• Discontinuation of offending medications - When possible 2

Important Clinical Pitfalls

1. Serum potassium is an inaccurate marker of total body potassium - Mild hypokalemia may reflect significant total body deficits 6

2. Risk of rebound hyperkalemia - Particularly when treating transcellular shifts 2

3. Chronic mild hypokalemia consequences - Can accelerate chronic kidney disease progression, exacerbate hypertension, and increase mortality 6

4. Potassium replacement in alkalosis - Should be given as potassium chloride to correct associated chloride deficit 3

5. Monitoring requirements - Regular serum potassium determinations are essential, especially in patients with renal insufficiency 4