Serum or plasma tests are performed to diagnose levels of potassium 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. Drugs can cause your kidneys to lose potassium, particularly diuretics (water pills), resulting in hypokalemia. Once your doctor discovers the reason for the too-high or -low potassium levels, s/he can start treating you.

Serum or plasma tests for potassium levels are routinely performed in most patients investigated for any type of serious illness. Also, because potassium is so important to heart function, it is a part of all complete routine evaluations, especially in those who take diuretics or heart medications, and in the investigation of high blood pressure and kidney disease. It is also used to monitor the patient receiving dialysis, diuretic therapy, or intravenous therapy.

Increased potassium levels indicate hyperkalemia. Increased levels may also indicate the following health conditions:

• 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;
• acute or chronic kidney failure;
• Addison’s disease;
• hypoaldosteronism;
• injury to tissue;
• infection;
• diabetes; and
• dehydration.

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 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, and
• deficient potassium intake (this is rare).

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.

PLEASE NOTE: Numerically reported test results are interpreted according to the test's reference range, which may vary by the patient's age, sex, as well as the instrumentation or kit used to perform the test. A specific result within the reference (normal) range – for any test – does not ensure health just as a result outside the reference range may not indicate disease. To learn more about reference ranges, please see the article, Reference Ranges and What They Mean. To learn the reference range for your test, consult your doctor or laboratorian. Lab Tests Online recommends you consult your physician to discuss your test results as a part of a complete medical examination.

The way that your blood is drawn and handled may cause the potassium level in the sample to be falsely high. If you clench and relax your fist a lot while your blood is drawn, this will make potassium rise. If blood comes out of your veins too fast or too slow, the blood cells can break and increase potassium. Sometimes, if more than one tube of blood is drawn at the same time, some potassium from the tubes with the purple tops can get into the other tubes and increase the potassium.

If the specimen does not get from your doctor’s office to the laboratory quickly, the potassium can also increase.

If there are any questions as to how your blood was collected, your doctor may request that the test be repeated before starting any treatment.