Test Overview

The phosphate urine test measures the amount of phosphate in a sample of urine collected over 24 hours (24-hour urine test). Phosphate is a charged particle (ion) that contains the mineral phosphorus. The body needs phosphorus to build and repair bones and teeth, help nerves function, and make muscles contract. Most (about 85%) of the phosphorus contained in phosphate is found in bones. The rest of it is stored in tissues throughout the body.

The kidneys help control the amount of phosphate in the body. Extra phosphate is filtered by the kidneys and passes out of the body in the urine. If there is not enough phosphate, less is found in the urine. Kidney problems can cause high or low levels of phosphate in the urine. High levels of phosphate in the urine also may be caused by eating a meal high in phosphorus or having an overactive parathyroid gland. Some types of tumors may also cause high levels of phosphate in the urine.

Tests for calcium and creatinine levels may be done at the same time as a phosphate urine test.

Why It Is Done

A test to measure phosphate in urine may be done to:

• Help diagnose kidney problems that affect phosphate levels.
• Help find the cause of kidney stones.

How To Prepare

• In general, there's nothing you have to do before this test, unless your doctor tells you to.
• For 24-hour urine collection, your doctor or lab will usually give you a large container that holds about 1 gallon.

How It Is Done

This test is usually done at home. You must collect all the urine you produce in a 24-hour period.

• When you first get up in the morning, urinate into the toilet. Don't save this urine. Write down the time that you urinated. This marks the start of your 24-hour period.
• For the next 24 hours, collect all your urine. Your doctor or lab will give you a large container to store it in. The container may have a small amount of preservative in it. Urinate into a separate small, clean container. Then pour the urine into the large container. Don't touch the inside of the containers with your fingers.
• Keep the large container in the refrigerator.
• Empty your bladder for the last time at or just before the end of the 24-hour period. Add this urine to the large container, and write down the time.
• Do not get toilet paper, pubic hair, stool (feces), menstrual blood, or anything else in your urine sample.

How It Feels

This test usually doesn't cause any pain or discomfort.

Risks

There are no known risks from having this test.

Results

Normal

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

High values

High urine phosphate levels may be caused by:

• Kidney diseases.
• An overactive parathyroid gland (hyperparathyroidism).

Low values

Low urine phosphate levels may be caused by:

• An underactive parathyroid gland (hypoparathyroidism).
• Kidney or liver diseases.
• Severe malnutrition.