Potassium

What is potassium?

Potassium is one of the most important electrolytes in the body, and most of it is found inside cells. For nerve impulses to be transmitted, for muscles to contract and especially for the heart to beat regularly, the potassium level in the blood must be kept within a narrow range. Potassium also contributes to maintaining the body's fluid and acid-base balance. Many foods, such as bananas, dried legumes, potatoes and green leafy vegetables, are rich in this mineral.

Excess potassium from the daily diet is excreted in the urine by the kidneys; this process is regulated by the hormone aldosterone, which is secreted by the adrenal glands. Some hormones, such as insulin, also affect the movement of potassium into cells. The test is measured in the serum or plasma portion of the blood using a method called an ion-selective electrode and is usually ordered together with other electrolytes such as sodium and chloride.

When is a potassium test ordered?

Potassium is one of the basic tests included in routine biochemistry panels. Because both high and low potassium can affect heart rhythm, it is measured regularly, especially in people with heart disease, kidney disease or high blood pressure. Your doctor may also repeat the test at set intervals when starting, and during, treatment with medications that can change potassium levels. It is also one of the first tests checked in fluid losses such as prolonged vomiting or diarrhea and in complaints related to heart rhythm.

• Muscle weakness, cramps or marked fatigue
• Palpitations or an irregular heart rhythm
• Prolonged vomiting, diarrhea or excessive fluid loss
• Use of diuretics, certain blood pressure medications or potassium supplements
• Kidney disease, uncontrolled diabetes or adrenal gland disorders

How do I prepare for a potassium test?

Potassium measurement does not require fasting, and blood can be given at any time of day; if fasting tests such as blood sugar are also being done on the same day, the morning is more practical. Repeatedly opening and closing your fist during the blood draw can cause potassium to move from the muscles into the blood and make the result falsely high. It is therefore recommended that you keep your hand relaxed during the procedure. For the same reason, it is also important that the tourniquet does not stay tight on your arm for a long time.

Because hemolysis or a long delay before processing can also cause potassium to leak out of cells, it is important that the blood sample is collected carefully and delivered to the laboratory without delay. Blood pressure medications, diuretics and potassium supplements can affect the result, so tell your doctor about the medications you take, but do not stop any of them on your own. You do not need to go to a healthcare facility to give blood; a nurse can take the sample at your home or workplace.

What does a potassium result mean?

High potassium, or hyperkalemia, is most commonly seen when the kidneys cannot excrete potassium adequately, in adrenal insufficiency, and with the use of certain blood pressure medications that reduce potassium excretion. Uncontrolled diabetes and extensive tissue damage can also raise the value. However, some high results may be due to blood collection and transport conditions, such as hemolysis of the blood sample or delayed processing; in this case your doctor may have the test repeated.

Low potassium, or hypokalemia, mostly develops due to vomiting, diarrhea, diuretic use, frequent use of laxatives or certain hormonal disorders; low magnesium may also accompany it. Because both a marked elevation and a marked decrease can affect heart rhythm, your doctor may want to evaluate the result promptly. Your potassium result should be assessed against the range of the laboratory that analyzed the test, shown on this page, because reference values can vary between laboratories depending on the method, age and sex. The person who will interpret your result, taking into account your medications, your symptoms and your other tests, is your doctor.