Serum potassium, K

This is a blood test to measure the amount of potassium in your blood. Potassium is one of several important minerals in your body called electrolytes. Ninety percent of your potassium is inside your cells, but a small amount moves around in your blood. You normally get potassium from the foods you eat. Your body needs a constant level of potassium for normal nerve conduction, muscle contraction, heart function, and fluid balance. Your kidneys remove potassium through your urine.

You may need this test if you are having routine blood test to check your level of electrolytes. You may also need this test if your doctor suspects that your potassium is too high or too low. It's important to have your potassium level checked if you have diabetes, if you have a disease that affects your kidneys, adrenal glands, or digestive system, or if you are on medicines, such as diuretics, steroids, or digitalis.

A potassium level that is too high is called hyperkalemia. Symptoms of hyperkalemia include:

• Irregular heartbeat
• Nausea
• Fatigue
• Tingling or numbness
• Weakness or paralysis

A potassium level that is too low is called hypokalemia. Symptoms of hypokalemia include:

• Irregular heartbeat
• Nausea
• Muscle weakness
• Cramps
• Muscle twitching
• Constipation

You may have your potassium checked along with other electrolytes, such as sodium. You may also have an electrocardiogram, or ECG, to check your heart rhythm. An irregular heart rhythm is a dangerous sign if caused by an abnormal potassium level.

Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your doctor what your test results mean for you.

Potassium is measured in milliequivalents per liter (mEq/L). Normal results are about:

• 3.5 to 5.2 mEq/L for adults.
• 3.4 to 4.7 mEq/L for children ages 1 to 18 years old.

Low blood potassium may be caused by:

• Loss of potassium due to diarrhea, excessive laxative use, sweating, or vomiting.
• Not getting enough potassium in your diet. This is sometimes seen in alcoholism.
• Loss of potassium from a severe burn or draining wound.
• Diseases, such as cystic fibrosis, primary aldosteronism, or alcoholism.
• Medicines, such as diuretics or antibiotics.
• Getting I.V. fluids without enough potassium.

High blood potassium may be caused by:

• Kidney disease or kidney failure.
• Trauma, such as burns, accidents, or surgery.
• Uncontrolled diabetes.
• Diseases, such as lupus, sickle cell, or Addison disease.

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand.

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore.

Several medicines can affect your potassium level. These include penicillin, glucose, diuretics, such as furosemide or hydrochlorothiazide, and nonsteroidal anti-inflammatory drugs (NSAIDS). Eating a lot of licorice can decrease potassium levels.

You don't need to prepare for this test. Tell your doctor if you are taking any medicine, including over-the-counter NSAIDs. Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.