Phosphate in Urine

What is a phosphate in urine test?

A phosphate in urine test measures the amount of phosphate in a urine (pee) sample that you collect over a 24-hour period. Phosphate is an electrolyte. Electrolytes are electrically charged minerals. They help control the amount of fluid and the balance of acids and bases (pH balance) in your body.

Phosphate is made of the mineral phosphorous combined with oxygen. Phosphate works with the mineral calcium to build strong bones and teeth. Most of your phosphate is stored in your bones. But phosphate is in every cell of your body and it affects almost everything your cells do, including how your nerves work and how your body uses energy.

Most people get more phosphate than they need from food. Your kidneys control the amount of phosphate in your blood by removing most of the extra phosphate through your urine. Your parathyroid glands in your neck make hormones which affect how much phosphate your kidneys remove.

If you have a problem with your kidneys or your parathyroid glands, the phosphate levels in your urine may be too high or too low. This can be a sign of a serious health problem.

Other names: phosphorous test, P, PO4, inorganic phosphate, PO4 urine concentration

What is it used for?

A phosphate in urine test may be used to help:

• Diagnose kidney problems
• Diagnose disorders of the parathyroid glands
• Find out if too much phosphate in urine is causing kidney stones, small, pebble-like material that form in the kidneys

Why do I need a phosphate in urine test?

You may need a phosphate in urine test if you have:

• Symptoms of a kidney problem
• Had a kidney stone
• Problems with your electrolyte balance, which affects your acid/base (pH) level
• Had abnormal results on a calcium test

Calcium and phosphate work together, so problems with calcium levels can mean problems with phosphate levels as well. Calcium testing in blood and/or urine is often part of a routine checkup.

What happens during a phosphate in urine test?

You'll need to collect all your urine during a 24-hour period. This is called a 24-hour urine sample test. You will be given a special container to collect your urine and instructions on how to collect and store your sample. Your health care provider will tell you what time to start. The test generally includes the following steps:

• To begin, urinate in the toilet as usual. Do not collect this urine. Write down the time you urinated.
• For the next 24 hours, collect all your urine in the container.
• During the collection period, store the urine container in a refrigerator or in a cooler with ice.
• 24 hours after starting the test, try to urinate if you can. This is the last urine collection for the test.
• Return the container with your urine to your provider's office or the laboratory as instructed.

Will I need to do anything to prepare for the test?

You don't need any special preparations for a phosphate in urine test. Be sure to carefully follow all the instructions for providing a 24-hour urine sample.

Are there any risks to the test?

There is no known risk to having a phosphate in urine test.

What do the results mean?

The terms phosphate and phosphorous are both used to mean the same thing in test results. So, your results may say "phosphorous levels" or "phosphate levels." Your results may include guidelines for normal, low, and high levels, but your provider will consider your health, age, and other factors when deciding what is normal for you.

High phosphate/phosphorous levels in your urine may mean you have:

• Kidney disease
• Hyperparathyroidism, a condition in which your parathyroid gland produces too much parathyroid hormone.
• Too much vitamin D in your body, usually from taking too many supplements

Low phosphate/phosphorous levels in your urine may mean you have:

• Kidney disease
• Liver disease
• Hypoparathyroidism, a condition in which your parathyroid gland produces too little parathyroid hormone

Your provider will likely order other tests to help make a diagnosis. If your phosphate/phosphorous levels are not normal, it doesn't always mean you have a medical condition that needs treatment. Eating a meal high in phosphorous or using laxatives with sodium phosphate can affect your results. Also, children often have higher phosphate levels because their bones are still growing. If you have questions about your results, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a phosphate in urine test?

Phosphate is often tested in blood. Your provider may order both a blood and urine test to see how much phosphate your kidneys are removing.