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 contains the mineral phosphorus. So, a phosphate test is sometimes called a phosphorus test.

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. Your body also needs phosphates for many other important processes, such as:

• Building strong bones and teeth. Most of the phosphate in your body is found in your bones where it is combined with the mineral calcium.
• Making energy.
• Helping your nerves and muscles work properly.

The phosphorus in phosphate comes from the foods you eat, including nuts and seeds, dairy products, dried beans, meats, poultry, and eggs. Your body tightly controls the amount of phosphate in your blood mainly through your:

• Kidneys. They filter extra phosphate from your blood and get rid of it through urine (pee). If your phosphate level is low, your kidneys limit the amount lost through urine.
• Intestines. They control how much phosphorus you absorb from the foods you eat.

The amount of phosphate in your body is also linked to your levels of:

• Calcium. When calcium levels increase, phosphate levels decrease. And when calcium levels decrease, phosphate levels increase.
• Vitamin D. It helps your body use phosphate.
• Parathyroid hormone (PTH). This hormone is made by parathyroid glands in your neck. It helps balance phosphate and calcium levels.

Abnormal phosphate levels may be a sign of problems with the systems in your body that control phosphate levels. These include various kidney conditions and disorders of the parathyroid glands.

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

What is it used for?

Your health care provider may use a phosphate in urine test, along with other tests, to help:

• Understand the cause of high or low phosphate in your blood.
• Find out if too much phosphate in urine is causing kidney stones, small, pebble-like material that form in the kidneys.
• Diagnose kidney problems.
• Diagnose disorders of the parathyroid glands.

Why do I need a phosphate in urine test?

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

• Had an abnormal result on a phosphate in blood test.
• Had a kidney stone.
• Had an abnormal result on a blood or urine calcium test. Calcium and phosphate work together, abnormal calcium levels may mean you have abnormal phosphate levels, too.
• Symptoms of a kidney problem.
• Problems with your electrolyte balance, which affects your acid/base (pH) level.

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 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 results of your phosphate test may say "phosphorus levels" or "phosphate levels." These terms mean the same thing. 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.

To understand what your test results mean, your provider will consider your symptoms, medical history, and the results of other tests. That's why it's best to ask your provider what your test results say about your health. In general:

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

• Kidney disease that affects your kidneys' ability to hold on to phosphate.
• Hyperparathyroidism, a condition in which your parathyroid gland produces too much parathyroid hormone.

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

• Kidney disease that affects your kidneys' ability to get rid of extra phosphate.
• Hypoparathyroidism, a condition in which your parathyroid gland produces too little parathyroid hormone.

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. A laxative is a medicine that can help you have a bowel movement (poop). 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.