Blood Potassium Level
Blood Potassium Level
Potassium is a mineral that is found in abundance in the body, primarily within its cells. Only about 2% of the body’s total potassium is not within its cells. Potassium levels are crucial to the appropriate functioning of all cells, especially nerve and muscle cells. For the body to function normally, blood potassium levels have to be maintained at a very narrow range; when potassium levels are too high or too low, there can be serious health consequences. The body keeps its potassium levels in equilibrium by prompting the kidneys to resorb more (when the body needs potassium) or excrete more (when there is excess potassium). The hormone responsible for stimulating the processing of potassium in the kidneys is called aldosterone. Aldosterone is secreted by the adrenal glands. When blood potassium levels get too high, the condition is called hyperkalemia. When blood potassium levels get too low, the condition is called hypokalemia.
A blood potassium level is usually drawn as part of a larger panel of electrolytes. Other measurements in the electrolyte panel include sodium, chloride, and carbon dioxide. A blood potassium level is usually checked during a regular physical examination, when there are concerns about the functioning of the patient’s kidneys, when the patient has high blood pressure (hypertension), to monitor potassium levels during the use of medications that affect its equilibrium (such as certain diuretics, which cause potassium to be lost in the urine), in patients on dialysis, in patients who are on intravenous fluids or receiving parenteral nutrition, and in patients who have symptoms such as unexplained weakness or abnormal heart rhythms (cardiac arrhythmias).
Blood potassium levels can be affected by a number of medications. Patients who are on these medications should inform their doctor, so that test results can be interpreted appropriately. Medications that increase blood potassium levels include some chemotherapy agents, aminocaproic acid, high blood pressure medications (specifically angiotensin-converting enzyme or ACE inhibitors), certain diuretics (referred to as potassium-sparing or potassium-conserving diuretics), epinephrine, heparine, histamine, isoniazid, mannitol, and succinylcholine. Medications that decrease blood potassium levels include acetazolamide, aminosalicylic acid, amphotericin B, carbenicillin, cisplatin, potassium-wasting diuretics (such as thiazide diuretics and furosemide), insulin, laxatives, penicillin G, phenothiazines, salicylates, and sodium polystyrene sulfonate. Other factors that may skew the results of blood potassium level include intravenous infusion of fluids containing potassium, as well as intravenous infusion of either glucose-containing solutions or insulin.
Patients who are taking anticoagulant medications should inform their healthcare practitioner since this may increase their chance of bleeding or bruising after a blood test.
Addison’s disease— A condition in which the adrenal glands are not functioning properly. Addison’s disease can be caused by a problem in the adrenal glands themselves, or in the pituitary gland (which secretes a hormone that affects the adrenal glands.
Bartter’s syndrome— An inherited disorder which affects a number of body processes, including the functioning of the part of the kidney that regulates potassium excretion and absorption. People with Bartter’s syndrome have abnormally low blood potassium levels (hypokalemia).
Diuretic— A medication that increases the flow of urine through the kidneys and out of the body.
Hyperkalemia— Elevated blood potassium levels.
Hypokalemia— Low blood potassium levels.
Proper technique in drawing the potassium blood level and in handling the sample is crucial to an accurate result. If the patient is clenching and relaxing arm muscles in the arm from which the blood is being drawn, the potassium blood level may be falsely elevated. If the flow of blood into the vacuum tubes is not carefully regulated, and the blood flows too quickly or too slowly into the tubes, then the blood cells may be damaged due to turbulence. This will cause the blood cells to leak potassium into the sample, falsely elevating the result. Delay in testing the blood at the laboratory will also result in an artificially elevated blood potassium level being reported.
This test requires blood to be drawn from a vein (usually one in the forearm), generally by a nurse or phlebotomist (an individual who has been trained to draw blood). A tourniquet is applied to the arm above the area where the needle stick will be performed. The site of the needle stick is cleaned with antiseptic, and the needle is inserted. The blood is collected in vacuum tubes. After collection, the needle is withdrawn, and pressure is kept on the blood draw site to stop any bleeding and decrease bruising. A bandage is then applied.
There are no restrictions on diet or physical activity, either before or after the blood test.
As with any blood tests, discomfort, bruising, and/or a very small amount of bleeding is common at the puncture site. Immediately after the needle is withdrawn, it is helpful to put pressure on the puncture site until the bleeding has stopped. This decreases the chance of significant bruising. Warm packs may relieve minor discomfort. Some individuals may feel briefly woozy after a blood test, and they should be encouraged to lie down and rest until they feel better.
Basic blood tests, such as blood potassium levels, do not carry any significant risks other than slight bruising and the chance of brief dizziness.
In adults, a normal blood potassium level is 3.5–5.0 milliequivalents perliter (mEq/L) or 3.5–5.0 millimoles per liter (mmol/L). In children a normal blood potassium level is 3.4–4.7 mEq/L or 3.4–4.7 mmol/L. In infants, a normal blood potassium level is 4.13–5.3 mEq/L or 4.1-–5.3 mmol/L. In newborns, a normal blood potassium level is 3.9-5.9 mEq/L or 3.9–5.9 mmol/L.
High blood potassium levels may be due to:
- kidney disease, either acute or chronic kidney failure;
- Addison’s disease (a disease in which the adrenal gland is under-functioning);
- low blood levels of the hormone aldosterone, termed hypoaldosteronism;
- tissue injury, resulting in the release of potassium into the bloodstream, including trauma, heart attack, severe burns;
- excess intake of foods containing potassium (in particular, fruits and fruit juices are often high in potassium;
- excess intake of potassium supplements; or
- medications that elevate potassium, including NSAIDS (ibuprofen); beta blockers (propranlol and atenolol); ACE inhibitors (captopril, enlapril, lisinopril); and diruetics such as triamterene, amiloride, and spironolactone.
Low blood potassium levels may be due to:
- severe vomiting;
- severe diarrhea;
- insulin use;
- Cushing’s syndrome;
- cystic fibrosis;
- poor nutritional status due to alcoholism, eating disorder, and other causes of malnutrition;
- Bartter’s syndrome;
- too much aldosterone in the blood (hyperaldosteronism);
- diuretic use (thiazide diuretics and furosemide, in particular); or
- poor dietary intake of potassium.
Goldman L., D. Ausiello, eds. Cecil Textbook of Internal Medicine, 23rd ed. Philadelphia: Saunders, 2007.
McPherson R. A., and M. R. Pincus, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods, 21st ed. Philadelphia: Saunders, 2006.
Medical Encyclopedia. Medline Plus. U.S. National Library of Medicine and the National Institutes of Health. January 2, 2008. http://www.nlm.nih.gov/medlineplus/encyclopedia.html (February 10, 2008).
American Association for Clinical Chemistry, 1850 K Street, NW, Suite 625, Washington, DC, 20006, (800) 892-1400, http://www.aacc.org.
Rosalyn Carson-DeWitt, M.D.