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Phosphate in Urine

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 also may be caused by eating a meal high in phosphorus, having high levels of vitamin D in your body, or by an overactive parathyroid gland.

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

Calcium and phosphate levels are often measured at the same time.

Many medicines can change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

How It Is Done

Urine phosphate is usually measured in a sample taken from all the urine produced in a 24-hour period.

To collect your urine for 24 hours:

  • You start collecting your urine in the morning. When you first get up, empty your bladder but do not save this urine. Write down the time that you urinated to mark the beginning of your 24-hour collection period.
  • For the next 24 hours, collect all your urine. Your doctor's office or lab will usually provide you with a large container that holds about 1 gal (4 L). The container has a small amount of preservative in it. Urinate into a small, clean container and then pour the urine into the large container. Do not touch the inside of the container with your fingers.
  • Keep the large container in the refrigerator for the 24 hours.
  • Empty your bladder for the final time at or just before the end of the 24-hour period. Add this urine to the large container and record the time.
  • Do not get toilet paper, pubic hair, stool (feces), menstrual blood, or other foreign matter in the urine sample.

How It Feels

There is no pain while collecting a 24-hour urine sample.

Risks

There is no chance for problems while collecting a 24-hour urine sample.

Results

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.

Normal

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Results are usually available in 1 to 2 days.

Phosphate in urine1
Adults:

0.4–1.3 grams (g) per 24-hour urine sample

13–42 millimoles (mmol) per day
Calcium- and phosphate-restricted diet:

Less than 1.0 g per 24-hour urine sample

Less than 32 mmol per day

 

Many conditions can change phosphate levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.

High values

High urine phosphate levels may be caused by:

Low values

Low urine phosphate levels may be caused by:

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

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Taking certain medicines, such as diltiazem (such as Cardizem), aspirin, corticosteroids, diuretics, or parathyroid hormone.
  • Taking a lot of antacids.
  • Not collecting all of your urine within the 24-hour collection period.

What To Think About

  • Phosphate may also be measured in the blood. For more information, see the topic Phosphate in Blood.
  • Results of a test to measure phosphate in urine are seldom useful on their own. They should always be interpreted along with the results of other tests.
  • The loss of too much phosphate into the urine may cause conditions that damage the bones, such as rickets or osteomalacia.

References

Citations

  1. Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.

Credits

By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer Alan C. Dalkin, MD - Endocrinology
Last Revised September 30, 2011

Last Revised: September 30, 2011

Author: Healthwise Staff

Medical Review: E. Gregory Thompson, MD - Internal Medicine & Alan C. Dalkin, MD - Endocrinology

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