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Alternative namesHypokalemia test; K+
DefinitionThis test measures the amount of potassium in the blood.
How the test is performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to swell with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
How to prepare for the testThe health care provider may advise you to withhold drugs that may affect the test. (See special considerations.)
Infants and children:
The preparation you can provide for this test depends on your child's age, previous experience, and level of trust. For general information regarding how you can prepare your child, see the following:
How the test will feelWhen the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
Potassium (K+) is the major positive ion within cells and is particularly important for maintaining the electric charge on the cell membrane. This charge allows nerves and muscles to communicate and is necessary for transporting nutrients into cells and waste products out of the cell. The concentration of potassium inside cells is about 30 times that in the blood and other fluids outside of cells.
Metabolic acidosis (for example, caused by uncontrolled diabetes) or alkalosis (for example, caused by excess vomiting) can affect blood potassium.
Small changes in the potassium concentration outside cells can have substantial effects on the activity of nerves and muscles. This is particularly true of heart muscle. Low levels of potassium cause increased activity (which can lead to an irregular heartbeat ), whereas high levels cause decreased activity. Either situation can lead to cardiac arrest in some circumstances.
In normal people, taking potassium supplements or potassium-containing drugs is of no consequences, because the kidneys efficiently dispose of excess potassium.
Normal ValuesThe normal range is 3.7 to 5.2 mEq/L.
Note: mEq/L = milliequivalent per liter
What abnormal results meanGreater-than-normal levels of potassium ( hyperkalemia ) may indicate:
What the risks areRisks associated with venipuncture are slight:
Special considerationsThe following factors can interfere with the test:
Drugs that can increase potassium measurements include aminocaproic acid, antineoplastic drugs, ACE inhibitors (such as captopril or enalapril) epinephrine, heparin, histamine, isoniazid, mannitol, some diuretics, and succinylcholine.
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. If puncturing the vein is difficult, trauma to the red blood cells may cause potassium to be released from them, causing a falsely elevated result.
Update Date: 9/15/2003Irfan A. Agha, M.D., Department of Medicine, Renal Division, St. Louis University, St. Louis, MO. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT