As part of a routine medical exam, when you have symptoms such as weakness and/or cardiac arrhythmia, or when an electrolyte imbalance is suspected; at regular intervals when you are taking a medication and/or have a disease or condition, such as high blood pressure (hypertension) or kidney disease, that can affect your potassium level
A blood sample drawn from a vein in the arm
Potassium is an electrolyte, a positively charged molecule that works with other electrolytes, such as sodium, chloride, and bicarbonate (total CO2) to help regulate the amount of fluid in the body, stimulate muscle contraction, and maintain a stable acid-base balance. Potassium is present in all body fluids, but most potassium is found within your cells. Only about two percent is present in fluids outside the cells and in the liquid part of the blood (called serum or plasma). Because the blood concentration of potassium is so small, minor changes can have significant consequences. If potassium levels go too low or too high, your health may be in considerable danger: you are at risk for developing shock, respiratory failure, or heart rhythm disturbances. An abnormal concentration can alter the function of neuromuscular tissue; for example, the heart muscle may lose its ability to contract.
How is the sample collected for testing?
A blood sample is taken by needle from a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
Potassium testing is frequently ordered, along with other electrolytes, as part of a routine physical. It is used to detect concentrations that are too high (hyperkalemia) or too low (hypokalemia). The most common cause of hyperkalemia is kidney disease, but many drugs can decrease potassium excretion from the body and result in this condition. Hypokalemia can occur if you have diarrhea and vomiting or if you are sweating excessively. Potassium can be lost through your kidneys in urine; in rare cases, potassium may be low because you are not getting enough in your diet.
Potassium concentrations may be ordered at regular intervals to monitor drugs that can cause your kidneys to lose potassium, particularly diuretics, resulting in hypokalemia. Monitoring may also be done if you have a condition or disease, such as acute or chronic kidney failure, that can be associated with abnormal potassium levels.
When is it ordered?
serum or plasma tests for potassium levels are routinely performed in most patients when they are investigated for any type of serious illness. Also, because potassium is so important to heart function, it is usually ordered (along with other electrolytes) during all complete routine evaluations, especially in those who take diuretics or or blood pressure or heart medications. Potassium is ordered when a doctor is diagnosing and evaluating high blood pressure (hypertension) and kidney disease and when monitoring a patient receiving dialysis, diuretic therapy, or intravenous therapy.
What does the test result mean?
Increased potassium levels indicate hyperkalemia. Increased levels may also indicate the following health conditions:
- acute or chronic kidney failure
- Addison's disease
- hypoaldosteronism (see Aldosterone)
- injury to tissue
- excessive dietary potassium intake (for example, fruits are particularly high in potassium, so excessive intake of fruits or juices may contribute to high potassium)
- excessive intravenous potassium intake
Certain drugs can also cause hyperkalemia in a small percent of patients. Among them are non-steroidal anti-inflammatory drugs (such as Advil, Motrin, and Nuprin); beta blockers (such as propanolol and atenolol), angiotensin-converting enzyme inhibitors (such as captopril, enalapril, and lisinopril), and potassium-sparing diuretics (such as triamterene, amiloride, and spironolactone).
Decreased levels of potassium indicate hypokalemia. Decreased levels may occur in a number of conditions, particularly:
- Hyperaldosteronism (see Aldosterone)
- deficient potassium intake (rare)
- as a complication of acetaminophen overdose
In diabetes, your potassium may fall after you take insulin, particularly if your diabetes had been out of control for a while. Low potassium is commonly due to “water pills” (diuretics); if you are taking these, your doctor will check your potassium level regularly.
Additionally, certain drugs such as corticosteroids, beta-adrenergic agonists such as isoproterenol, alpha-adrenergic antagonists such as clonidine, antibiotics such as gentamicin and carbenicillin, and the antifungal agent amphotericin B can cause loss of potassium.
Is there anything else I should know?
Physicians question elevated potassium results when the numbers do not fit the patients clinical condition. Potassium levels can be falsely elevated by the following specimen-collection or processing errors:
- Clenching and relaxing your fist a lot while your blood is drawn.
- Collecting the specimens without regard for the proper order of draw of the tubes; that is, drawing a tube that has an anticoagulant containing potassium prior to a non-anticoagulated tube. This results in specimen contamination of the non-anticoagulated tube with potassium.
- Delayed handling or processing of the specimen. The red cells and serum or plasma need to be separated within the appropriate clot to centrifugation time. This also reduces error if the specimen has to be transported from your doctors office to a laboratory.
- Improper centrifugation
- Any action that can cause the red cells to break apart (hemolyze) and release more potassium into the specimen. This may include using a large diameter needle (causes the blood to enter the evacuate collection tube with too much force), inverting the tube too vigorously, drawing the blood through a small needle, and using a syringe with excessive suction applied to the plunger.
- Crying and hyperventilation can either increase or decrease the plasma potassium level.
If there are any questions as to how your blood was collected, your doctor may request that the test be repeated to verify results.
What are some good dietary sources of potassium?Low levels of potassium can be a result of increased urinary loss due to certain heart medications that lower sodium levels and prevent water retention. To make up for this loss of potassium, doctors often suggest eating more foods high in potassium. A number of fruits and vegetables (bananas, cantaloupe, grapefruit, oranges, tomatoes, honeydew melons, potatoes) and meats are good sources of potassium.
Is there an over-the-counter test I can use to check my potassium levels?