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, having high levels of vitamin D in your body, 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

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:

  • Start 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 urine footnote 1
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.
    To learn more, 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

ByHealthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD – Internal Medicine
Specialist Medical Reviewer Alan C. Dalkin, MD – Endocrinology

Current as ofMay 3, 2017