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Potassium (K+), serum or plasma

3.5–5.0 meq/L [mmol/L]

Panic: <3.0 or > 6.0 meq/L

SST, green


Avoid hemolysis.

Physiologic Basis

Potassium is predominantly an intracellular cation whose plasma level is regulated by renal excretion.

Plasma potassium concentration determines neuromuscular irritability. Elevated or depressed potassium concentrations interfere with muscle contraction.


Increased in: Massive hemolysis, severe tissue damage, rhabdomyolysis, acidosis, dehydration, acute or chronic renal failure, Addison disease, renal tubular acidosis type IV (hyporeninemic) hypoaldosteronism, (hyperkalemic) familial periodic paralysis, pseudohypoaldosteronism (types I and II), congenital adrenal hyperplasia (salt-wasting form), exercise (transient). Drugs: potassium salts, potassium-sparing diuretics (eg, spironolactone, triamterene, eplerenone), nonsteroidal anti-inflammatory drugs, β-blockers, ACE inhibitors, ACE-receptor blockers, high-dose trimethoprim-sulfamethoxazole, pentamidine, verapamil.

Decreased in: Low potassium intake, prolonged vomiting or diarrhea, renal tubular acidosis types I and II, hyperaldosteronism, Cushing syndrome, osmotic diuresis (eg, hyperglycemia), alkalosis, (hypokalemic) familial periodic paralysis, trauma (transient), subarachnoid hemorrhage, genetic hypokalemic salt-losing tubulopathies such as Gitelman syndrome (familial hypokalemia-hypocalciuria-hypomagnesemia). Drugs: adrenergic agents (isoproterenol), diuretics.


Spurious hyperkalemia can occur with hemolysis of sample, delayed separation of serum from erythrocytes, prolonged fist clenching during blood drawing, and prolonged tourniquet placement. Very high white blood cell or platelet counts may cause spurious elevation of serum potassium, but plasma potassium levels are normal.

Ben Salem C et al. Drug-induced hyperkalemia. Drug Saf 2014;37:677.  [PMID: 25047526]

Jain G et al. Genetic disorders of potassium homeostasis. Semin Nephrol 2013;33:300.  [PMID: 23953807]

Lee Hamm L et al. Acid-base and potassium homeostasis. Semin Nephrol 2013;33:257.  [PMID: 23953803]

Medford-Davis L et al. Derangements of potassium. Emerg Med Clin North Am 2014;32:329.  [PMID: 24766936]

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McPhee, Stephen J., et al. "Potassium." Guide to Diagnostic Tests, 7th ed., McGraw-Hill Education, 2017. Medicine Central, im.unboundmedicine.com/medicine/view/GDT/619256/all/Potassium.
McPhee SJ, Lu CM, Nicoll D. Potassium. Guide to Diagnostic Tests. 7th ed. McGraw-Hill Education; 2017. https://im.unboundmedicine.com/medicine/view/GDT/619256/all/Potassium. Accessed April 26, 2019.
McPhee, S. J., Lu, C. M., & Nicoll, D. (2017). Potassium. In Guide to Diagnostic Tests. Available from https://im.unboundmedicine.com/medicine/view/GDT/619256/all/Potassium
McPhee SJ, Lu CM, Nicoll D. Potassium [Internet]. In: Guide to Diagnostic Tests. McGraw-Hill Education; 2017. [cited 2019 April 26]. Available from: https://im.unboundmedicine.com/medicine/view/GDT/619256/all/Potassium.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Potassium ID - 619256 A1 - McPhee,Stephen J, AU - Lu,Chuanyi Mark, AU - Nicoll,Diana, BT - Guide to Diagnostic Tests UR - https://im.unboundmedicine.com/medicine/view/GDT/619256/all/Potassium PB - McGraw-Hill Education ET - 7 DB - Medicine Central DP - Unbound Medicine ER -