Phosphorus measurement, urine
What is this test?
This test measures the amount of phosphorus (a mineral) in urine. This test is used to identify phosphorus as a possible cause of kidney stones. It is also used when hyperphosphaturia (increased phosphorus levels in urine) is suspected.
What are related tests?
- Kidney stone analysis
- Serum inorganic phosphate measurement
Why do I need this test?
Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. You may need this test if you have:
- Elevated phosphate in urine
- Kidney stone
When and how often should I have this test?
When and how often laboratory tests are done may depend on many factors. The timing of laboratory tests may rely on the results or completion of other tests, procedures, or treatments. Lab tests may be performed immediately in an emergency, or tests may be delayed as a condition is treated or monitored. A test may be suggested or become necessary when certain signs or symptoms appear.
Due to changes in the way your body naturally functions through the course of a day, lab tests may need to be performed at a certain time of day. If you have prepared for a test by changing your food or fluid intake, lab tests may be timed in accordance with those changes. Timing of tests may be based on increased and decreased levels of medications, drugs or other substances in the body.
The age or gender of the person being tested may affect when and how often a lab test is required. Chronic or progressive conditions may need ongoing monitoring through the use of lab tests. Conditions that worsen and improve may also need frequent monitoring. Certain tests may be repeated to obtain a series of results, or tests may need to be repeated to confirm or disprove results. Timing and frequency of lab tests may vary if they are performed for professional or legal reasons.
How should I get ready for the test?
During a 24-hour urine collection, follow your usual diet and drink fluids as you ordinarily would, unless healthcare workers give you other instructions. Avoid drinking alcohol before and during the urine collection.
How is the test done?
For a 24-hour urine collection, all of the urine that you pass over a 24-hour time period must be collected. If you are in the hospital, a healthcare worker will collect your urine. You will receive a special container to collect the sample in if you are doing the collection at home. The following are directions for collecting a 24-hour urine sample while at home:In the morning scheduled to begin the urine collection, urinate in the toilet and flush away the first urine you pass. Write down the date and time. That is the start date and time for the collection.Collect all urine you pass, day and night, for 24 hours. Use the container given to you to collect the urine. Avoid using other containers. The urine sample must include the last urine that you pass 24 hours after starting the collection. Do not allow toilet paper, stool, or anything else to be added to the urine sample.Write down the date and time that the last sample is collected. The urine sample may need to be kept cool during the 24-hour collection period. If so, keep the closed container in a pan on ice. Do not put ice in the container with the urine.
How will the test feel?
The amount of discomfort you feel will depend on many factors, including your sensitivity to pain. Communicate how you are feeling with the person doing the test. Inform the person doing the test if you feel that you cannot continue with the test.
This test usually causes no discomfort.
What should I do after the test?
When 24-hour urine collection is complete, close the container and seal the lid tightly. Return the sample in the urine container to the facility or healthcare worker as instructed. If you had the sample in an ice bath, return the sample within two hours after removing the container from the ice bath.
What are the risks?
Urine: A urine test is generally considered safe. Talk to your healthcare worker if you have questions or concerns about this test.
What are normal results for this test?
Laboratory test results may vary depending on your age, gender, health history, the method used for the test, and many other factors. If your results are different from the results suggested below, this may not mean that you have a disease. Contact your healthcare worker if you have any questions. The following is considered to be a normal result for this test:
Adults (varies with intake): 400 -1300 mg/24 hours (12.9-42 mmol/24 hours) 
What follow up should I do after this test?
Ask your healthcare worker how you will be informed of the test results. You may be asked to call for results, schedule an appointment to discuss results, or notified of results by mail. Follow up care varies depending on many factors related to your test. Sometimes there is no follow up after you have been notified of test results. At other times follow up may be suggested or necessary. Some examples of follow up care include changes to medication or treatment plans, referral to a specialist, more or less frequent monitoring, and additional tests or procedures. Talk with your healthcare worker about any concerns or questions you have regarding follow up care or instructions.
Where can I get more information?
- Linus Pauling Institute's Micronutrient Information Center - http://lpi.oregonstate.edu/infocenter/index.html
- National Kidney and Urologic Diseases Information Clearinghouse - http://kidney.niddk.nih.gov/
- National Kidney Foundation - http://www.kidney.org
 Muezzinoglu T, Gumus B, Sener E, et al: The diagnostic value of the phosphate levels in serum and 24-hour urine samples in patients with recurrent renal stone disease. Scand J Urol Nephrol 2002; 36(5):368-372.
 Rodgers AL, Barbour LJ, Pougnet BM, et al: Re-evaluation of the "week-end effect" data: possible role of urinary copper and phosphorus in the pathogenesis of renal calculi. J Trace Elem Med Biol 1995; 9(3):150-155.
 Salem RR & Tray K: Hepatic resection-related hypophosphatemia is of renal origin as manifested by isolated hyperphosphaturia. Ann Surg 2005; 241(2):343-348.
 Vanderlinde RE & Kowalski P: The clinical biochemistry of phosphorus. Clin Biochem 1971; 4(2):76-88.
 Kratz A, Ferraro M, Sluss PM, et al: Case records of the Massachusetts General Hospital: laboratory values. N Engl J Med 2004; 351(15):1549-1563.
Last Updated: 7/4/2018