Potassium test

Potassium test

Definition:

A test that measures the amount of potassium in the blood.

Alternative Names:

Hypokalemia test; K+

How the test is performed:

Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (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 tourniquet to distend (fill 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 tourniquet 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.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

Occasionally, in people experiencing periodic episodes of paralysis, the potassium level may be drawn during an attack of paralysis.

How to prepare for the test:

The health care provider may advise you to withhold drugs that may affect the test (see special considerations).

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:

infant test or procedure preparation (birth to 1 year)
toddler test or procedure preparation (1 to 3 years)
preschooler test or procedure preparation (3 to 6 years)
schoolage test or procedure preparation (6 to 12 years)
adolescent test or procedure preparation (12 to 18 years)

How the test will feel:

When 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:

This test is performed to evaluate blood levels of potassium.

Potassium (K+) is the major positive ion within cells and is particularly important for maintaining the electric charge on the cell membrane, which is necessary for neuromuscular communication and 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 extracellular fluids.

Potassium levels are mainly controlled by the steroid hormone aldosterone (for more information see the aldosterone test), which increases excretion of potassium. Aldosterone is secreted from the adrenal gland in the presence of increasing levels of potassium. Metabolic acidosis (for example, caused by uncontrolled diabetes) or alkalosis (for example, caused by excess vomiting) can affect blood potassium because this ion shifts into or out of cells in exchange for hydrogen ions. For example, in acidosis some of the excess hydrogen ions will shift into cells in exchange for potassium ions being released from the cells.

Small changes in the potassium concentration outside cells can have substantial effects on the activity of nerves and muscles. This is particularly true of the heart muscle. Low levels of potassium cause increased activity (which can lead to an arrhythmia), 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 Values:

The normal range is 3.7 to 5.2 mEq/L.

Note: mEq/L = milliequivalent per liter

What abnormal results mean:

Greater-than-normal levels (hyperkalemia) may indicate:

Addison's disease (rare)
crush injury (tissue trauma)
hemolysis (red blood cell destruction)
hypoaldosteronism (very rare)
metabolic or respiratory acidosis
renal failure
transfusion of hemolyzed blood
hyperkalemic periodic paralysis (potassium is elevated during episodes of paralysis)

Lower-than-normal levels (hypokalemia) may indicate:

Cushing's syndrome (rare)
deficient potassium intake in the diet
diarrhea
hyperaldosteronism (very rare)
renal tubular acidosis (rare)
vomiting
excessive potassium loss because of a GI (gastrointestinal)disorder -- e.g., villous adenoma (tumor)
hypokalemic periodic paralysis (low potassium during an episode of paralysis)
diuretic use

Additional conditions under which the test may be performed:

What the risks are:

Risks associated with venipuncture are slight:

excessive bleeding
fainting or feeling light-headed
hematoma (blood accumulating under the skin)
infection (a slight risk any time the skin is broken)
multiple punctures to locate veins

Special considerations:

Interfering factors:

infusion of potassium-containing fluids
infusion of glucose or insulin

Drugs that can increase potassium measurements include aminocaproic acid, antineoplastic drugs, angiotensin converting enzyme inhibitors, such as captopril or enalapril, epinephrine, heparin, histamine, isoniazid, mannitol, some diuretics, and succinylcholine.

Drugs that can decrease potassium measurements include acetazolamide, aminosalicylic acid, amphotericin B, carbenicillin, cisplatin, some diuretics, insulin, laxatives, penicillin G, phenothiazines, salicylates, and sodium polystyrene sulfonate.

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.

Review Date: 11/7/2001
Reviewed By: Jeffrey Heit, M.D., Department of Medicine, University of Pennsylvania Health System, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is the first of its kind, requiring compliance with 53 standards of quality and accountability, verified by independent audit. A.D.A.M. is among the first to achieve this important distinction for online health information and services. A.D.A.M. is also a founding member of Hi-Ethics (www.hiethics.com) and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 2003 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.