Laboratory Studies
Laboratory studies include the following:
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Serum potassium level < 3.5 mEq/L (3.5 mmol/L) [5]
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BUN and creatinine level
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Glucose, calcium, and/or phosphorus level if coexistent electrolyte disturbances are suspected.
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Magnesium levels are unreliable and typically do not change management, since patients with hypokalemia almost always have coincident hypomagnesemia and should be treated empirically.
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Consider digoxin level if the patient is on a digitalis preparation; hypokalemia can potentiate digitalis-induced arrhythmias.
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Consider arterial blood gas (ABG): Alkalosis can cause potassium to shift from extracellular to intracellular.
Imaging Studies
Computed tomography (CT) scanning of the adrenal glands is indicated if mineralocorticoid excess is evident (rarely needed emergently).
Other Tests
Electrocardiography
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T-wave flattening or inverted T waves
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Prominent U wave that appears as QT prolongation (see the image below)
Prominent U waves after T waves in hypokalemia.
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ST-segment depression
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Ventricular arrhythmias (eg, premature ventricular contractions [PVCs], torsade de pointes, ventricular fibrillation) [4]
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Atrial arrhythmias (eg, premature atrial contractions [PACs], atrial fibrillation)
Thyroid screening studies - Thyroid-stimulating hormone (TSH), free T3, and free T4 in patients with tachycardia, especially Asian patients [6]
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Prominent U waves after T waves in hypokalemia.
