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For further information, see CMDT Part 21-04: Hypokalemia

Key Features

Essentials of Diagnosis

  • Serum K+ < 3.5 mEq/L (< 3.5 mmol/L)

  • Severe hypokalemia may induce arrhythmias and rhabdomyolysis

  • Assessment of urine potassium excretion (urine potassium to creatinine ratio) can distinguish renal from non-renal loss of potassium

General Considerations

  • Hypokalemia can result from

    • Insufficient dietary potassium intake

    • Intracellular shifting of potassium from the extracellular space

    • Potassium loss (renal or extra-renal)

  • A low dietary potassium intake is usually not sufficient to cause hypokalemia because the kidneys can lower urine potassium excretion to very low levels (< 15 mEq/L)

  • Shift of potassium into cells is increased by insulin and beta-adrenergic stimulation

  • Excess potassium excretion by the kidneys is usually due to increased aldosterone action in the setting of preserved delivery of sodium to the distal nephron

  • Magnesium

    • An important regulator of potassium handling

    • Low levels lead to persistent renal excretion of potassium; hypokalemia is often refractory to treatment until the magnesium deficiency is corrected

  • Loop diuretics (eg, furosemide) cause substantial renal potassium and magnesium losses

Clinical Findings

  • Usually asymptomatic

  • When severe, may lead to muscle weakness and cardiac arrhythmias

  • Involvement of gastrointestinal smooth muscle may result in constipation or ileus

  • Rhabdomyolysis with associated acute kidney injury may occur with potassium levels < 2.5 mEq/L

  • May additionally present as polyuria and polydipsia due to diminished concentrating ability of the kidney (nephrogenic DI)

  • Chronic hypokalemia can lead to kidney disease (tubulointerstitial nephritis)


Laboratory Tests

  • Transient hypokalemia is generally secondary to intracellular shift, while sustained hypokalemia is secondary to potassium wasting or rarely inadequate intake

  • Assessment of renal potassium excretion can help distinguish renal from non-renal causes

  • A 24-hour urine collection is the most accurate method for assessing renal handling of potassium, with a level < 25 mEq/day compatible with appropriate renal potassium retention, and higher values corresponding to renal potassium wasting

  • A more immediate assessment can be made by measuring a urine potassium to creatinine ratio (UK/UCr) on a spot urine sample

  • In the setting of hypokalemia, a UK/UCr ratio < 13 mEq/g (or 1.5 mEq/mmol) is suggestive of a nonrenal etiology, most commonly gastrointestinal losses, intracellular potassium shifts, or inadequate dietary intake; higher values imply renal potassium wasting

Diagnostic Procedures

  • Characteristic progression of electrocardiogram (ECG) changes as the hypokalemia becomes more severe: initially T wave flattening, subsequently ST depressions and T wave inversions, ultimately U waves

  • Typical ECG patterns may be not be observed in all patients


  • Any underlying conditions should be treated and causative drugs discontinued

  • Magnesium deficiency should be corrected, particularly in refractory hypokalemia

  • Oral potassium supplementation

    • Safest for mild to ...

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