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.
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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 , diuretic therapy, or
intravenous therapy.
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What does the test result mean?
Increased potassium levels indicate
hyperkalemia. Increased levels may also indicate the following health conditions:
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:
- dehydration
- vomiting
- diarrhea
- 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.
NOTE: The result of your potassium test is measured by your doctor against a reference range for the test to determine whether the result is “normal” (it is within the range of numbers), high (it is above the high end of the range), or low (it is below the low end of the range). Because there can be many variables that affect the determination of the reference range, the reference range for this test is specific to the lab where your test sample is analyzed. For this reason, the lab is required to report your results with an accompanying reference range. Typically, your doctor will have sufficient familiarity with the lab and your medical history to interpret the results appropriately
While there is no such thing as a “standard” reference range for potassium, most labs will report a similar, though maybe not exactly the same, set of numbers as that included in medical textbooks or found elsewhere online. For this reason, we recommend that you talk with your doctor about your lab results. For general guidance only, we are providing the below from the classic medical text, Tietz Textbook of Clinical Chemistry and Molecular Diagnostics.
For more information on reference ranges, please read Reference Ranges and What They Mean.
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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.
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