Fast Five Quiz: Electrolyte Disorders

Vecihi Batuman, MD


March 23, 2021

Prescription medications that increase urination (diuretics) are the most common cause of hypokalemia. Excessive potassium loss can also result from vomiting or diarrhea. Other causes include:

The symptoms of hypokalemia are nonspecific and are predominantly related to muscular or cardiac function. Weakness and fatigue are most common. Physical examination findings are often within the reference range. Hypertension in patients with hypokalemia may indicate primary hyperaldosteronism; renal artery stenosis; licorice ingestion; or the more unusual forms of genetically transmitted hypertensive syndromes, such as congenital adrenal hyperplasia, glucocorticoid-remediable hypertension, or Liddle syndrome. Relative hypotension in patients with hypokalemia should suggest occult laxative use; diuretic use; bulimia; or one of the unusual genetic tubular disorders, such as Bartter syndrome or Gitelman syndrome.

In most cases, the cause of hypokalemia is apparent from the history and physical examination. However, measurement of urine potassium is vital because it establishes the pathophysiologic mechanism behind hypokalemia and thus aids in formulating the differential diagnosis. A serum magnesium assay is also important in the differential diagnosis, as well as in therapy, and is therefore performed as a first-line test.

Perform ECG to determine whether the hypokalemia is affecting cardiac function or to detect digoxin toxicity. The following tests may be appropriate but should not be first-line tests, unless the clinical index of suspicion for the disorder is high:

  • Drug screen in urine and/or serum for diuretics, amphetamines, and other sympathomimetic stimulants

  • Serum renin, aldosterone, and cortisol

  • 24-hour urine aldosterone, cortisol, sodium, and potassium

  • Pituitary imaging to evaluate for Cushing syndrome

  • Adrenal imaging to evaluate for adenoma

  • Evaluation for renal artery stenosis

  • Enzyme assays for 17-beta hydroxylase deficiency

  • Thyroid function studies in patients with tachycardia, especially Asian patients

  • Serum anion gap (eg, to detect toluene toxicity)

Usually, oral potassium chloride is administered when potassium levels need to be replenished, as well as in patients with ongoing potassium loss (eg, those on thiazide diuretics), in whom it must be maintained. Potassium-sparing diuretics are generally used only in patients with normal renal function who are prone to significant hypokalemia.

ACE inhibitors, which inhibit renal potassium excretion, can ameliorate some of the hypokalemia that thiazide and loop diuretics can cause. However, ACE inhibitors can lead to severe hyperkalemia in patients with renal insufficiency who are taking potassium supplements or potassium-sparing diuretics.

Read more about hypokalemia.


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