Summary

• Potassium is an electrolyte that you get from the food you eat.
• It works together with sodium to keep the fluids in your body in balance.
• Your kidneys use sodium and potassium as a way of controlling how much water stays in your blood and how much is removed through your urine.
• By controlling the amount of water in your blood, potassium also helps to control your blood pressure.
• Potassium and sodium are needed to make nerve signals such as those telling your muscles to contract and relax.
• Potassium is important in keeping your heart rhythm steady

What is potassium and how does your body use it?

Potassium is an electrolyte. Electrolytes are minerals that carry an electrical charge in fluids. In your body, they help regulate many systems including heart rhythms, nerve impulses and muscles contractions.

Potassium is in all body fluids, but most is inside your cells with only a very small amount in your blood. Because the amount of potassium in your blood is so small, even tiny changes in levels can have a big impact on your health.

You take in potassium from the food in your diet, and excess potassium is removed by your kidneys and passed into your urine. Your kidneys maintain a consistent level of potassium by adjusting the amount kept in the blood and how much goes into the urine.

Your kidneys use sodium and potassium to help balance your body’s fluids

You have a pair of kidneys located just at the bottom of your ribcage on either side of your spine. Inside each kidney are about a million tiny blood filtering units. These filter your blood and remove wastes and excess water from your body. Water is sent to your bladder to be removed as urine.

When your kidneys filter out water from your blood, the amount of water that is kept in your bloodstream and the amount that is passed into your urine to be removed can be adjusted.

Your kidneys use sodium and potassium as a way of controlling how much water stays in your blood.

Sodium pulls water into your blood through a process called osmosis. If your kidneys hold on to more sodium, this draws more water into the bloodstream. See more on sodium.

This extra water in your blood increases the amount of blood in your circulation. Having more blood increases the pressure in your arteries and veins. More blood pushing against your blood vessel walls raises your blood pressure.

How potassium works together with sodium

In your kidneys, potassium and sodium are exchanged for each other. When potassium goes into the kidney cells, sodium is pushed out into your urine.

More potassium in your kidneys means less sodium. Less sodium means less water and lower blood pressure.

Potassium also helps relax blood vessel walls. It is part of a feedback system of hormones that control blood pressure. For more on how this works see Aldosterone and renin.

How sodium and potassium work to control your body’s fluid balance

Sodium and potassium keep the fluid levels inside and outside your cells in balance.

• Potassium is mainly found inside your body’s cells
• Sodium is mainly found outside the cells
• Sodium pulls water out of cells
• Potassium pulls water into cells

This:

• Keeps cells the right size
• Stops them swelling or shrinking due to dehydration
• Keeps the circulating blood volume and blood pressure stable

There is a lot more sodium than potassium in the bloodstream, so sodium has a big effect on circulating blood volume and therefore blood pressure.

There is much more potassium inside cells, so potassium controls cell hydration and electrical function.

Nerve signals and muscle movement

Nerves send electrical signals so you can feel touch and pain and control your muscle movements. For example, when your brain tells your hand to pick up a cup, electricity carries the messages from your brain to your hand. This is rather like an electrical cable, except the electrical signals jump from one cell to another.

Sodium and potassium are needed to do this. They make an electrical charge through what is called the sodium-potassium pump.

This works by letting sodium and potassium move in and out of a cell in a precise sequence, creating an electrical change. Sodium and potassium in one cell create an electrical signal that jumps to the next cell, which responds by creating another electrical signal that jumps to the next cell, and so on. In this way, the nerve impulse travels along the nerve like a wave. Once the electrical impulse has passed the cell is reset ready for the next impulse.

Heart rhythm

Sodium and potassium work as electrical partners that control the heart’s rhythm and its strength of contraction.

• At the start of a heartbeat, sodium enters the heart cells which creates an electrical spike that triggers contraction of the heart muscle.
• Potassium then leaves the heart cells which stops and resets the cells and allows the heart to be ready for the next beat.
• This sequence of events happens with every heartbeat. If the process is disturbed it can cause irregular heart rhythms.

Why get tested?

Potassium is a component of the electrolyte test, which is used for general health checks and is one of the most commonly ordered blood tests.

Electrolyte tests are most often ordered:

• As part of a group of tests called the kidney function test which includes creatinine and urea to check how well your kidneys are working.
• Together with Liver Function Tests (LFTs), a group of tests used to assess your liver.
• To investigate and monitor treatment of high blood pressure, diabetes and liver and kidney disease.
• To investigate possible heart problems and monitor treatment of heart failure.
• To monitor your health if you are taking blood pressure medication, diuretics or heart medications, and if you are on kidney dialysis or receiving intravenous therapy on a drip.
• In emergency situations such as when there is chest pain, palpitations or irregular heartbeat, ECG abnormalities, heart failure or heart attack because even small potassium changes can quickly cause dangerous heart rhythm problems.

Having the test

Sample

Blood.

Any preparation?
None.

Your results

Reference intervals - comparing your results to the healthy population

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people.
• They are used to provide a benchmark for interpreting a patient's test results.
• When compared against them, your results may be flagged high or low if they sit outside this range.
• Some reference intervals are harmonised or standardised, which means all labs in Australia use them.
• Others are not because for these tests, labs are using different instruments and chemical processes to analyse samples.
• Always compare your lab results to the reference interval provided on the same report.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation.

Any more to know?

The way that your blood is taken 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 being collected, this can make potassium rise. If blood comes out of your veins too fast or too slow, the blood cells can burst and release potassium into the blood, giving a falsely raised potassium result. Potassium can also be elevated if the specimen takes a long time to travel from your GP surgery or collection centre to the laboratory.

Several fruits, vegetables and meats are good sources of potassium. Examples include bananas, melons, oranges, potatoes, spinach, broccoli, milk, yoghurt, turkey and beef.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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