A potassium test is used to detect abnormal concentrations of potassium, including high potassium (hyperkalemia) and low potassium (hypokalemia). It is often used as part of an electrolyte panel or basic metabolic panel for a routine physical.

Potassium is an electrolyte that is vital to cell metabolism. It helps transport nutrients into cells and removes waste products out of cells. It is also important in muscle function, helping to transmit messages between nerves and muscles, and is important to heart function.

The potassium test may be used to help diagnose and/or monitor kidney disease, the most common cause of high blood potassium. It may also be used to evaluate for abnormal values when someone has diarrhea and vomiting, excessive sweating, or with a variety of symptoms. Blood potassium can be abnormal in many diseases. A healthcare practitioner may order this test, along with other electrolytes, to identify an electrolyte imbalance, if metabolic acidosis is suspected, or if there is high blood pressure or other symptoms of illness present. Potassium in particular may be measured when there are symptoms involving the heart.

The potassium test may also be used to monitor effects of drugs that can cause the kidneys to lose potassium, particularly diuretics, or drugs that decrease potassium elimination from the body and result in high potassium.

Urine potassium levels may be tested in people who have abnormal blood potassium levels to help determine the cause, such as dehydration. Urine potassium testing is also used for people with abnormal kidney tests to help the healthcare practitioner determine the cause of kidney disease and to help guide treatment.

Potassium levels may be ordered when people undergo a routine medical exam or when they are being evaluated for a serious illness.

Testing may be done when a person has:

• Kidney disease
• Symptoms such as muscle weakness or irregular heart beat (cardiac arrhythmia)
• A condition treated with diuretics or heart medications
• Has high blood pressure (hypertension) or is being treated for high blood pressure

Potassium testing may be ordered at regular intervals when a healthcare practitioner is diagnosing and evaluating hypertension, diabetic ketoacidosis, and kidney disease and when monitoring a patient receiving dialysis, diuretic therapy, or intravenous fluids.

Urine potassium testing may be done when blood potassium levels are abnormal.

High potassium levels (hyperkalemia) may be seen in conditions such as:

• Kidney disease
• Addison disease
• Injury to tissue
• Infection
• Diabetes
• Dehydration
• Consuming too much potassium (for example, fruits are particularly high in potassium, so excessive intake of fruits or juices may contribute to high potassium)
• In patients on intravenous (IV) fluids, excessive IV potassium
• Certain drugs can also cause high potassium in a small percent of people; among them are non-steroidal anti-inflammatory drugs (NSAIDs), ACE inhibitors, 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).

Low potassium levels (hypokalemia) may be seen in conditions such as:

• Diarrhea and vomiting
• Conn syndrome (hyperaldosteronism)
• A complication of acetaminophen overdose
• In diabetes, the potassium level may fall after someone takes insulin, particularly if the person has not managed his or her diabetes well.
• Low potassium is commonly due to "water pills" (potassium-wasting diuretics); if someone is taking these, their healthcare provider will check their 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.

Potassium urine concentrations must be evaluated in association with blood levels. The body normally eliminates excess potassium, so the concentration in the urine may be elevated because it is elevated in the blood. It may also be elevated in the urine when the body is losing too much potassium; in this case, the blood level would be normal to low. If blood potassium levels are low due to insufficient intake, then urine concentrations will also be low.

• Decreased urinary potassium levels may be due to certain drugs such as NSAIDs, beta blockers, and lithium or due to the adrenal glands producing too little of the hormone aldosterone.
• Increased urinary potassium levels may be due to kidney disease, eating disorders such as anorexia, or muscle damage.

Potassium levels can be falsely elevated by a variety of circumstances surrounding specimen collection and specimen processing. For example, if someone is clenching and relaxing his or her fist, the potassium level in the blood may increase. If blood samples are delayed in getting to the lab or if the blood tubes are subjected to vigorous shaking or rough handling in transit, potassium may leak from red blood cells and falsely elevate the potassium in the serum. A healthcare practitioner may question elevated potassium results when the numbers do not fit the clinical condition. If there are any questions as to how the blood was collected, the healthcare practitioner may request that the test be repeated to verify results.