Renal/Urology · PANCE / PANRE

Hypokalemia

Serum K <3.5 mEq/L; commonly from GI/renal losses; replace K and Mg.

Also known as: hypokalemia, low potassium

Overview

Serum potassium concentration <3.5 mEq/L. Severity: mild 3.0-3.4, moderate 2.5-2.9, severe <2.5. May reflect total body deficit (GI/renal loss, inadequate intake) or transcellular shift (alkalosis, insulin, beta-agonists).

Epidemiology

Most common electrolyte abnormality in clinical practice. Affects ~20% of hospitalized patients. Strong association with diuretic use, hyperaldosteronism, GI losses, and certain endocrine and renal tubular disorders.

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Risk factors

Diuretics: thiazide (HCTZ, chlorthalidone, indapamide), loop (furosemide, torsemide, bumetanide)
GI losses: vomiting, diarrhea, NG suction, laxative abuse
Renal: hyperaldosteronism (primary, secondary), Cushing syndrome, Liddle syndrome, Bartter/Gitelman syndromes, RTA types 1 and 2
Magnesium deficiency (renders K replacement ineffective)
Transcellular shift: alkalosis (each 0.1 pH rise lowers K ~0.4), insulin, beta-2 agonists (albuterol), refeeding syndrome, hypokalemic periodic paralysis
Decreased intake (rare alone): anorexia, alcoholism
Drugs: amphotericin B, aminoglycosides, cisplatin, high-dose penicillins

Pathophysiology

Total body potassium deficit develops from loss exceeding intake (GI, renal) or from intracellular shift. Hypokalemia hyperpolarizes excitable membranes, prolongs repolarization (QT prolongation, U waves), and increases risk of re-entrant arrhythmia. In skeletal muscle, severe hypokalemia causes weakness and rhabdomyolysis. Renal tubular damage from chronic hypokalemia can cause nephrogenic DI.

Clinical presentation

Symptoms

Mild: often asymptomatic
Moderate: weakness, fatigue, muscle cramps, constipation
Severe: flaccid paralysis (ascending), rhabdomyolysis, ileus, respiratory muscle weakness
Cardiac: palpitations, syncope from arrhythmia
Polyuria, polydipsia (nephrogenic DI from chronic hypokalemia)

Signs / physical exam

Hyporeflexia in severe hypokalemia
Hypotension (with concurrent volume depletion)
Hypertension if hyperaldosteronism etiology
Cardiac arrhythmias (premature beats, supraventricular and ventricular tachyarrhythmias, torsades de pointes if hypomagnesemia)
Ileus

Classic findings

ECG: T-wave flattening or inversion, prominent U waves, ST depression, prolonged QT, possible AV block; predisposes to torsades especially with hypomagnesemia.

Differential diagnosis

Diuretic-induced — Recent thiazide/loop initiation; urine K elevated; usually correctable with K replacement and oral supplementation
GI loss (vomiting/diarrhea) — Recent GI illness; metabolic alkalosis (vomiting) or acidosis (diarrhea); urine K low (<20) if extrarenal
Primary hyperaldosteronism — Hypertension + hypokalemia + metabolic alkalosis; aldosterone/renin ratio >20 with elevated aldosterone
Bartter syndrome — Hereditary; hypokalemia + metabolic alkalosis + normal-low BP; loop-like; presents in childhood
Gitelman syndrome — Hereditary; hypokalemia + alkalosis + hypomagnesemia + hypocalciuria; thiazide-like; often diagnosed in adolescence/adulthood
RTA type 1 (distal) — Hypokalemia + non-gap metabolic acidosis + urine pH >5.5; kidney stones (calcium phosphate)
RTA type 2 (proximal) — Hypokalemia + non-gap acidosis + glycosuria/aminoaciduria (Fanconi syndrome)
Hypokalemic periodic paralysis — Episodic flaccid paralysis triggered by carbs/exercise; familial or thyrotoxic

Diagnostic workup

Diagnostic criteria

Serum K <3.5 mEq/L. Establish if renal vs extrarenal vs shift; assess concurrent acid-base, BP, and volume status to narrow differential.

Labs

BMP — serum K, BMP, magnesium (essential — Mg deficit causes refractory hypokalemia)
ABG or VBG for acid-base status
Urine K (spot or 24-h) and urine creatinine — TTKG or urine K:Cr ratio distinguishes renal from extrarenal loss
Urine K <20 mEq/L (spot) or <15 mEq/day (24-h) = extrarenal loss
Urine K >20 mEq/L or >25 mEq/day = renal loss
Plasma renin and aldosterone (aldo:renin ratio) if hypertension + hypokalemia
TSH if periodic paralysis suspected
Urine chloride (low in vomiting/contraction alkalosis; high in mineralocorticoid excess)

Imaging

Adrenal CT/MRI if primary hyperaldosteronism confirmed by labs

Diagnostic algorithm

Etiology Category	Urine K	Acid-Base	BP	Example
Extrarenal loss	Low (<20)	Acidosis (diarrhea) or normal	Variable	Diarrhea, laxative abuse
Vomiting / NG suction	Low-variable	Metabolic alkalosis	Often low	Bulimia, GI obstruction
Diuretic	High (>20)	Metabolic alkalosis	Variable	Thiazide, loop
Primary hyperaldosteronism	High	Metabolic alkalosis	HIGH	Conn adenoma
Bartter / Gitelman	High	Metabolic alkalosis	Normal/low	Inherited tubular defect
RTA type 1 or 2	High	Non-gap metabolic ACIDOSIS	Normal	Sjögren (RTA-1), Fanconi (RTA-2)
Transcellular shift	Low (no loss)	Alkalosis or insulin effect	Variable	Insulin, beta-agonist, refeeding

Differential diagnosis of hypokalemia by urine K, acid-base status, and blood pressure.

Treatment

First-line

Replete potassium — oral if mild-moderate (K-Cl tablets 40-80 mEq/day in divided doses), IV if severe, symptomatic, NPO, or unable to tolerate oral
IV KCl: typically max 10 mEq/h peripheral (40 mEq/L), max 20 mEq/h central; cardiac monitor for rates >10 mEq/h
Each 10 mEq KCl raises serum K ~0.1 mEq/L (modest); large total body deficit (often >200-400 mEq) may exist with serum K of 3.0
REPLACE MAGNESIUM concurrently — hypomagnesemia causes K wasting and renders K supplementation ineffective. Goal Mg >2.0 mg/dL.
Address underlying cause: stop laxative, switch diuretic, treat hyperaldosteronism
K-sparing diuretic — spironolactone, eplerenone, amiloride, triamterene — when ongoing renal losses
Dietary K — bananas, oranges, potatoes, leafy greens, salt substitutes

Second-line / adjunct

Primary hyperaldosteronism: spironolactone or eplerenone; adrenalectomy for unilateral adenoma
Bartter/Gitelman: K and Mg replacement; spironolactone or amiloride; NSAIDs (Bartter only)
RTA: bicarbonate replacement with K supplementation
Thyrotoxic periodic paralysis: treat hyperthyroidism, beta-blocker (non-selective), K cautiously
Refeeding syndrome: gradual nutritional advancement, prophylactic phosphorus, K, Mg, thiamine
Recheck K every 2-6 hours during active replacement

Complications

Cardiac arrhythmias: PVCs, atrial and ventricular tachyarrhythmias, torsades de pointes
Sudden cardiac death (especially with concurrent QT-prolonging medications)
Muscle weakness, rhabdomyolysis
Respiratory failure (severe)
Ileus, constipation
Nephrogenic diabetes insipidus, polyuria
Hypertension if etiology is mineralocorticoid excess
Digoxin toxicity (hypokalemia potentiates) — important in patients on digoxin

PANCE pearls

ALWAYS check and replace magnesium when treating hypokalemia. Hypomagnesemia causes renal K wasting and makes K supplementation ineffective.
Rule of thumb: each 10 mEq KCl raises serum K only ~0.1 mEq/L. Patients with serum K 3.0 often have a total body deficit of 200-400 mEq.
Hypokalemia potentiates digoxin toxicity even at therapeutic levels — maintain K >4 in patients on digoxin.
ECG: T-wave flattening, U waves, ST depression, QT prolongation, predisposing to torsades.
Hypertension + hypokalemia + metabolic alkalosis = think primary hyperaldosteronism (Conn syndrome). Check ARR.
Gitelman syndrome: hypokalemia + alkalosis + low Mg + low urinary calcium. Bartter syndrome: similar but with normal/high urinary calcium and presents earlier.

References

KDIGO 2020 — KDIGO Controversies Conference on Potassium Management in Kidney Disease
Mount Krapf — Disorders of Potassium Balance (Mount, in Brenner & Rector's The Kidney, 11th ed)

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