Potassium

Potassium is a mineral found throughout your body that is essential to your health. It is one of several electrolytes that helps control your body’s fluid levels, acid-base balance, and nerve and muscle activity.

Most potassium tests measure the amount of potassium in your blood, but a urine potassium test is used in some situations. These tests can determine whether you have normal levels of potassium. Potassium levels that are too high or too low can cause numerous symptoms and health risks.

Potassium can be measured individually, but it is often included in broader tests such as an electrolyte panel, renal panel, or basic or comprehensive metabolic panel.

Purpose of the test

Tests that measure potassium have multiple applications in clinical medicine. Whether potassium is tested alone or as part of a panel, it can be part of diagnosis, monitoring, and screening.

Diagnosis

After signs or symptoms of a health problem have occurred, diagnosis is the process of finding their cause. High or low potassium levels can cause multiple types of symptoms, which can prompt potassium testing. An imbalance in electrolytes can affect virtually all systems of the body, so panel tests are frequently used in the diagnosis process of many different disorders.

Because the kidneys are centrally involved in regulating potassium levels, a potassium test is often used to help evaluate the status of your kidneys. Potassium also plays an important role in healthy heart function. It is involved in the electric signal functioning of the heart muscle, so potassium levels are frequently checked if you have heart-related symptoms.

Monitoring

Potassium tests are also used for monitoring, which is testing that tracks your condition over time. When treatment is given for abnormal potassium levels, repeat testing can indicate how well that treatment is working. Repeat testing of potassium either alone or in a panel can also be part of ongoing evaluation of the kidneys or cardiovascular system.

Measuring potassium and other electrolytes is common for patients who are in the hospital or who are taking many different kinds of medications. A proper electrolyte balance is vital for maintaining fluid levels, acid-base balance, and overall health, so regular monitoring of potassium and other electrolytes is frequently done in these settings.

Screening

Screening is often called early detection because it is testing that happens before there are any signs or symptoms of a health problem.

Screening with potassium testing is most common in people who have higher risk for kidney or cardiovascular disease, such as people with diabetes or high blood pressure. This testing is not standard for healthy adults without this elevated risk, but some primary care doctors may include it as part of blood testing during normal checkups for adults.

When tested for screening, potassium is usually part of a panel that measures other electrolytes. Panel tests for screening may also include other proteins and compounds in the blood that can inform the doctor about kidney function.

What does the test measure?

A potassium test measures the amount of potassium that is present in a sample of either blood or urine.

Potassium is an essential nutrient that is found throughout the body and is necessary for healthy cell activity. Without potassium, the heart and other muscles cannot function.

Diet, made up of the foods and drinks you consume, is the source of potassium. Some people also obtain potassium from dietary supplements.

Under normal circumstances, your body absorbs and stores the potassium that it needs, and the kidneys remove any excess primarily through urine. In this way, a potassium measurement can detect disruptions to this process of how the body stores, uses, and excretes potassium.

Blood levels of potassium are frequently measured in a panel test along with other electrolytes including sodium, chloride, and bicarbonate.

In some urine potassium tests, creatinine is measured along with potassium. Creatinine is a waste material that is a byproduct of muscle activity. Creatinine is excreted at a relatively steady pace from day to day. Measuring creatinine normalizes the potassium excretion independent of how many fluids you consume before the test and how dilute your urine is without having to do a full 24-hour urine collection.

When should I get a potassium test?

There are diverse circumstances in which a potassium test can be prescribed.

For diagnosis, a potassium blood test is usually performed if you have symptoms that could be related to an abnormal potassium level. Examples of symptoms of high potassium include an irregular heartbeat, muscle weakness, and nausea. Low potassium can cause heartbeat changes, fatigue, muscle cramps and twitches, nausea, and constipation.

Measurement of electrolytes including potassium is frequently done if the doctor suspects that you have possible heart issues, kidney problems or a disturbance of the body’s acid-base balance.

In addition, electrolyte testing is common if you have general symptoms or are being evaluated in an emergency room or urgent care clinic. Because electrolytes play a role in all bodily functions, this testing, including measuring potassium, can help identify an underlying cause of pressing health problems.

Most potassium testing is blood testing, which is used to diagnose high potassium levels, known as hyperkalemia, or low potassium, which is called hypokalemia. However, in some cases, urine potassium testing is needed to help determine why levels are low.

For monitoring, potassium and other electrolyte tests may be repeated multiple times at regular intervals to detect any abnormal changes. This is often done for patients who are taking medications that can affect the kidneys or overall electrolyte balance. Patients taking diuretics or other intravenous drugs in the hospital may have frequent monitoring with electrolyte tests.

Screening for abnormal potassium levels typically occurs as part of a panel test that is performed during routine medical checkups. While doctors can prescribe this testing for any patient, it is usually reserved for people who have high blood pressure, diabetes, or a family history of kidney problems.

How to get tested

The standard potassium test uses a blood sample that is obtained with a blood draw at your doctor’s office, a hospital, or a laboratory.

Urine tests for potassium are less common. When needed, they are normally conducted with one of two methods:

• A 24-hour urine sample: This involves collecting all of the urine you produce over a full day so that the laboratory can measure the total amount of potassium you excreted during that time.
• A spot urine sample measuring the potassium-to-creatinine ratio: This method involves a one-time urine sample at a lab or medical office. Comparing the amount of potassium to creatinine in this sample allows the lab to estimate your 24-hour potassium excretion.

Blood and urine tests are done after being prescribed by a doctor or other health professional.

Can I take the test at home?

There are limited or no options for at-home kits to test potassium levels.

If you are prescribed a 24-hour urine test, you will need to collect your urine wherever you are during the day, including at home. However, this testing is still prescribed by your doctor rather than sold as a separate at-home test kit.

How much does the test cost?

The cost of a potassium test can change based on a number of factors including:

• Whether potassium is measured alone or as part of a panel test
• Whether the test uses a blood or urine sample
• Where the test sample is collected
• Whether your have health insurance coverage

The final cost of a potassium test can involve several components including charges for office visits, technician fees for taking your sample, and/or charges for laboratory evaluation.

Your insurance company may pay for some or all of these costs if your potassium test is prescribed by your doctor. For the most definitive information about likely costs, talk with your doctor’s office and medical insurance company.

Blood tests are the most common type of potassium test. For this test, a blood sample is taken in a medical lab, hospital, or doctor’s office.

For a urine potassium test, you may provide a one-time sample at a medical office or lab, or you may be asked to do a 24-hour sample in which you collect all of the urine you produce over the course of a day in special containers.

Before the test

If you are having a blood test for potassium alone, you usually will not have to follow any special preparation for the test. However, if you are having potassium tested as part of a panel test like a basic or comprehensive metabolic panel, you may need to fast for 8-12 hours beforehand. For this reason, you should check with your doctor about whether you can eat and drink before the blood draw.

For either a blood or urine test, you may need to temporarily stop taking certain medications beforehand. Some prescription or over-the-counter drugs as well as some dietary supplements can affect potassium levels. Your doctor can tell you whether you need to adjust your normal medications prior to your test.

During the test

For a potassium blood test, a blood sample will be taken from a vein in your arm. Most of the time, an elastic band called a tourniquet will be tied around your upper arm. This increases blood flow in your arm and makes it easier to access the vein.

The technician will use an antiseptic wipe on your skin near the vein and then insert a needle. A vial of blood will be withdrawn, and then the needle will be taken out.

The total blood draw usually lasts only a few minutes. There may be some pain during the procedure, and many people feel a brief sting when the needle is inserted.

For a spot urine test that measures the potassium-to-creatinine ratio, you will be given a receptacle to collect urine in the bathroom at the doctor’s office or lab. Normally you will be instructed to start urinating into the toilet and then collect a sample by holding the receptacle under your stream of urine.

For a 24-hour sample, you will be given bags or containers for collecting your urine for a full day. You will need to have a container with you through the day so that you can collect urine regardless of where you are.

For the standard 24-hour collection, you will start the day by urinating into the toilet after waking up. After that, you will collect all of your urine for the rest of the day and night. You will also collect the urine from when you first wake up the next day. After you have finished the 24-hour collection, you should follow the provided instructions for bringing your sample to the lab.

After the test

After a potassium blood test, a cotton swab or bandage will be placed over the puncture site to stop any bleeding. You can return to most normal activities once the test is over. Slight pain or bruising can affect your arm but normally goes away quickly.

There are few or no lasting effects from potassium urine tests. Once you have provided either a spot or 24-hour urine sample, you can engage in daily activities without restrictions.

Receiving test results

In most cases, results for both blood and urine potassium tests are available within a period of a few business days.

Test results can be sent by mail or made accessible through online health portals. You may also receive a call or email from your doctor to either review your results or to schedule a follow-up appointment.

Interpreting test results

Interpretation of a potassium test requires carefully considering the test result, the laboratory reference range, and your health situation. Because potassium is frequently measured with other electrolytes, levels may be evaluated together.

For a blood test, the test report should list the amount of potassium, which is measured in either milliequivalents per liter (mEq/L) or millimoles per liter (mmol/L). The test report will also show a reference range, which is what the laboratory considers to be an expected range for potassium levels.

A common reference range for potassium is from around 3.5 to 5 mmol/L, although there can be slight variation between laboratories. For this reason, it is important to look for the specific reference interval listed on your test report.

Too much potassium in the blood is called hyperkalemia. Hyperkalemia can be a sign that the kidneys are not properly removing excess potassium from the blood and excreting it from the body in urine. This is often related to the use of certain medications that prevent the kidneys from regulating potassium levels, but it may be caused by other kidney disorders.

High potassium levels can also occur when too much potassium is released into the blood from inside cells where it is normally stored. This can be caused by burns or other injuries as well as conditions that affect the acid-base balance in the body.

In many cases, high potassium levels are the result of multiple causes. Increasing potassium intake from diet or supplements rarely causes hyperkalemia alone, but, when paired with reduced kidney function or other contributing factors, increased intake may spur a rise in blood levels of potassium.

Too little potassium in the blood is known as hypokalemia. Hypokalemia most often can happen after taking diuretic medications that increase urination. Diarrhea, vomiting, and profuse sweating may also cause fluid loss that diminishes blood levels of potassium. Less often, hypokalemia is the result of insufficient potassium intake due to poor diet or health conditions that increase the amount of potassium stored in cells.

Urine potassium tests are normally only used if a blood potassium test is abnormal. For a urine potassium test, your test report will show either the total level of potassium measured in a 24-hour sample or the ratio of potassium to creatinine in a one-time urine sample.

As with a blood test, the report should show the laboratory’s reference range for urine potassium levels. Checking this reference range is important because there can be variation among laboratories depending on their measurement methods.

Causes of abnormal urine potassium levels are often similar to the causes that can affect blood potassium levels. When urine potassium is measured, it may help doctors identify the most likely cause of abnormal levels, including whether the kidney is properly enabling the excretion of potassium from the body.

Are test results accurate?

Blood tests for potassium are routinely used and are generally dependable for reflecting changes in total potassium levels.

There are certain factors that can affect the accuracy of potassium blood tests. Examples of these include:

• Fist clenching: Some people may tighten their hand into a fist multiple times before or during their blood draw, and this can create a brief boost in your measured potassium level that leads to a misleading test result.
• Difficulty drawing blood: If the technician struggles to access a vein in your arm, it may cause temporary damage to your red blood cells, releasing extra potassium from inside those cells into your blood. This can create a false elevation of potassium levels.
• Changes in blood cells: Patients with conditions that affect their white blood cell or platelet counts may have potassium blood test results that are falsely high or low. This can also be a result of certain medications that affect blood cell activity and production.

If your doctor suspects that one of these factors has affected your test, you may have a repeat potassium blood test with special measures taken to avoid potential inaccurate results.

For potassium urine tests, there are certain issues that can affect accuracy when using either a spot or 24-hour urine sample. One-time samples rely on a calculation of the potassium-to-creatinine ratio.

A 24-hour urine collection doesn’t rely on measuring creatinine, so it avoids these potential challenges. However, many people find the 24-hour sample to be inconvenient or difficult to collect. In many cases, this leads to them collecting too much or too little urine, either of which can affect the accuracy of the test.

Do I need follow-up tests?

Follow-up testing is common if you have abnormal levels of potassium in your blood.

In many cases, high or low potassium is found on routine testing or when you don’t have any notable symptoms. This can occur because mild changes in potassium levels do not always cause symptoms.

In these situations, follow-up usually involves a physical exam, a review of your health history, and a discussion of your current medications. These steps frequently are able to reveal a likely explanation for your potassium levels.

Common follow-up tests include an electrocardiogram (ECG), which is a test of heart function. This test is performed because of the potential effects of potassium levels on cardiovascular health. The doctor may also do other blood tests that evaluate your kidney function, acid-base balance, and other elements of your health.

You may have repeat testing of your blood potassium level to confirm the initial result or track your levels over time. In addition, a urine potassium test can be used as a follow-up test that helps to assess the most likely causes of abnormal potassium levels in your blood.

Questions for your doctor about test results

Asking questions can help you understand the meaning of your potassium test results. When you talk with your doctor, some of these questions may be helpful to review:

• Was my potassium level low, normal, or high?
• Were any other measurements taken along with potassium? If so, were they normal or abnormal?
• If my potassium was too high or too low, what do you think is the most likely cause?
• Are there any follow-up tests that you recommend?
• Should I have another potassium test?
• Should I make any changes to my diet?

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