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Potassium (K) in Blood

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Destruction of the red blood cells in the blood sample, which can happen when blood is taken or when it is being processed in the lab. When red blood cells are broken up, they release large amounts of potassium and can cause false high values.
  • Taking potassium supplements.
  • Taking medicines, such as antibiotics that contain potassium (such as a type of penicillin g), nonsteroidal anti-inflammatory drugs (NSAIDs), heparin, insulin, glucose, corticosteroids, diuretics, medicines used to treat high blood pressure and heart disease, and natural licorice (Glycyrrhiza glabra).
  • The overuse of laxatives.
  • Severe vomiting.

What To Think About

  • Low blood potassium values are more common than high blood potassium values.
  • An electrocardiogram (EKG or ECG) may show signs of a very high or very low blood potassium level because of the effect potassium has on the heart. To learn more, see the topic Electrocardiogram.
  • Other electrolyte tests, such as sodium, calcium, chloride, magnesium, phosphate, blood urea nitrogen (BUN), and creatinine, are often done at the same time as a test for potassium.

To learn more, see:

Sodium (Na) in Blood.
Calcium (Ca) in Blood.
Chloride (Cl).
Magnesium (Mg).
Blood Urea Nitrogen.
Creatinine and Creatinine Clearance.


  1. Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.

  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.

ByHealthwise Staff
Primary Medical ReviewerAdam Husney, MD - Family Medicine
Specialist Medical ReviewerAvery L. Seifert, MD - Urology
Last RevisedSeptember 4, 2012

WebMD Medical Reference from Healthwise

Last Updated: September 04, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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