Hypokalemia: workup and management
Serum potassium <3.5 mEq/L. Check the ECG and magnesium, replace potassium (oral when possible), and find the cause: GI losses, diuretics, transcellular shift or renal wasting. A spot urine potassium separates renal from non-renal losses.
Working diagnosis
Adult · US guidelines
Draft · awaiting physician review
01Orient
What's new in the evidence
- TIGHT K (2024): after cardiac surgery, a relaxed potassium target was noninferior to a tight high-normal target for atrial fibrillation
- Prefer oral replacement when K >2.5 mEq/L without severe features and the gut works
- Never give undiluted IV push potassium; use glucose-free fluid
Differential diagnoses
- Diuretics (thiazide, loop)
- GI losses: vomiting, diarrhea, laxatives, NG suction
- Transcellular shift: insulin, beta-agonists, alkalosis, refeeding
- Hypomagnesemia (makes hypokalemia refractory)
- Hyperaldosteronism (with hypertension)
- Renal tubular acidosis, Bartter or Gitelman syndrome
- Hypokalemic periodic paralysis (thyrotoxic) (can't miss)
02Assess
Risk scores and decision tools
- Spot urine potassium:creatinine ratio (>13 mEq/g = renal loss)
- Acid–base status to narrow the cause
- ECG: U waves, flattened T waves, QT prolongation
Key history questions
- Vomiting, diarrhea, laxative use
- Diuretics, insulin, beta-agonists, amphotericin, recent dietary change
- Weakness, cramps, palpitations
- Hypertension (aldosteronism)
- Poor intake, alcohol use, refeeding
Examination findings
- Muscle weakness, reduced reflexes
- Irregular pulse
- Blood pressure; volume status
03Investigate
Initial investigations
- ECG: U waves, flattened T waves, ST depression, arrhythmias
- BMP, magnesium, glucose
- Blood gas or bicarbonate (acid–base status)
Advanced investigations
- Spot urine potassium:creatinine ratio (>13 mEq/g suggests renal loss)
- Renin and aldosterone if hypertensive
- TSH if periodic paralysis suspected
04Treat
Immediate management
- K <2.5 mEq/L, ECG changes or symptoms: IV potassium chloride on cardiac monitoring
- Peripheral IV rate usually ≤10 mEq/h; up to 20 mEq/h via central line with monitoring
- Replace magnesium if low
First-line treatment
- Oral potassium chloride 40–100 mEq/day in divided doses for mild to moderate deficits
- Each 10 mEq raises serum potassium by roughly 0.1 mEq/L in normal kidney function (varies widely)
- Treat the cause; consider potassium-sparing diuretic if ongoing diuretic losses
Second-line treatment
- Thyrotoxic periodic paralysis: cautious potassium (rebound hyperkalemia risk) and nonselective beta-blocker
Specialist referrals
- Endocrinology for suspected aldosteronism or periodic paralysis
- Nephrology for unexplained renal potassium wasting
05Disposition
Admission criteria
- K <2.5 mEq/L or ECG changes or arrhythmia
- Muscle weakness or paralysis
- Ongoing losses needing IV replacement
Safe discharge criteria
- Mild hypokalemia with a clear cause and oral replacement
- Repeat level arranged
Follow-up timing
- Repeat potassium within 3–7 days
Patient instructions
- Take potassium with food and water
- Return for weakness or palpitations
Monitoring
- Potassium 2–4 hours after IV replacement
- Magnesium
Clinical pearls and pitfalls
- Hypokalemia will not correct until magnesium is replaced
- Avoid dextrose-containing fluids for IV potassium; insulin release lowers potassium further
RefGuidelines and landmark evidence
For education only. Typical adult starting points; confirm doses against renal function, allergies, interactions and your institution's protocols. Not a substitute for clinical judgment or senior review.