Phosphorus, Urine

Phosphorus, Urine

Synonym/acronym: Urine phosphate.

Common use

To assist in evaluating calcium and phosphorus levels related to use of diuretics in progression of renal disease.


Urine (5 mL) from an unpreserved random or timed specimen collected in a clean plastic collection container.

Normal findings

(Method: Spectrophotometry) Reference values are dependent on phosphorus and calcium intake. Phosphate excretion exhibits diurnal variation and is significantly higher at night.
Conventional UnitsSI Units (Conventional Units × 0.0323)
400–1,300 mg/24 hr12.9–42 mmol/24 hr


Phosphorus, in the form of phosphate, is distributed throughout the body. Approximately 85% of the body’s phosphorus is stored in bones; the remainder is found in cells and body fluids. It is the major intracellular anion and plays a crucial role in cellular metabolism, maintenance of cellular membranes, and formation of bones and teeth. Phosphorus also indirectly affects the release of oxygen from hemoglobin by affecting the formation of 2,3-bisphosphoglycerate. Levels of phosphorus are dependent on dietary intake.

Analyzing urinary phosphorus levels can provide important clues to the functioning of the kidneys and other major organs. Tests for phosphorus in urine usually involve timed urine collections over a 12- or 24-hr period. Measurement of random specimens may also be requested. Children with thalassemia may have normal phosphorus absorption but increased excretion, which may result in a phosphorus deficiency.

This procedure is contraindicated for



  • Assist in the diagnosis of hyperparathyroidism
  • Assist in the evaluation of calcium and phosphorus balance
  • Assist in the evaluation of nephrolithiasis
  • Assist in the evaluation of renal tubular disease

Potential diagnosis

Increased in

  • Abuse of diuretics (related to increased renal excretion)
  • Primary hyperparathyroidism (parathyroid hormone [PTH] increases renal excretion)
  • Renal tubular acidosis
  • Vitamin D deficiency (related to decreased renal reabsorption)

Decreased in

    Hypoparathyroidism (PTH enhances renal excretion; therefore, a lack of PTH will decrease urine phosphorus levels) Pseudohypoparathyroidism (PTH enhances renal reabsorption; therefore, a lack of response to PTH, as in pseudohypoparathyroidism, will decrease urine phosphorus levels) Vitamin D intoxication (vitamin D promotes renal excretion of phosphorus)

Critical findings


Interfering factors

  • Drugs and vitamins that can cause an increase in urine phosphorus levels include acetazolamide, acetylsalicylic acid, bismuth salts, calcitonin, corticosteroids, dihydrotachysterol, glucocorticoids, hydrochlorothiazide, mestranol, metolazone, parathyroid extract, and parathyroid hormone.
  • Drugs that can cause a decrease in urine phosphorus levels include aluminum-containing antacids and diltiazem.
  • Urine phosphorus levels are subject to diurnal variation: Output is highest in the afternoon, which is why 24-hr urine collections are recommended.
  • All urine voided for the timed collection period must be included in the collection or else falsely decreased values may be obtained. Compare output records with volume collected to verify that all voids were included in the collection.

Nursing Implications and Procedure


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching:   Inform the patient this test can assist in evaluating calcium and phosphorus balance.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s endocrine and genitourinary systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Review the procedure with the patient. Provide a nonmetallic urinal, bedpan, or toilet-mounted collection device. Address concerns about pain and explain that there should be no discomfort during the procedure.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Usually a 24-hr time frame for urine collection is ordered. Inform the patient that all urine must be saved during that 24-hr period. Instruct the patient not to void directly into the laboratory collection container. Instruct the patient to avoid defecating in the collection device and to keep toilet tissue out of the collection device to prevent contamination of the specimen. Place a sign in the bathroom to remind the patient to save all urine.
  • Instruct the patient to void all urine into the collection device and then to pour the urine into the laboratory collection container. Alternatively, the specimen can be left in the collection device for a health-care staff member to add to the laboratory collection container.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Instruct the patient to avoid excessive exercise and stress during the 24-hr collection of urine.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.


  • Potential complications: N/A
  • Ensure that the patient has complied with activity restrictions and pretesting preparations; assure that excessive exercise and stress have been restricted during the 24-hr procedure.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection.
  • Random Specimen (Collect in Early Morning)

  • Clean-Catch Specimen
  • Instruct the male patient to (1) thoroughly wash his hands, (2) cleanse the meatus, (3) void a small amount into the toilet, and (4) void directly into the specimen container.
  • Instruct the female patient to (1) thoroughly wash her hands; (2) cleanse the labia from front to back; (3) while keeping the labia separated, void a small amount into the toilet; and (4) without interrupting the urine stream, void directly into the specimen container.
  • Indwelling Catheter

  • Put on gloves. Empty drainage tube of urine. It may be necessary to clamp off the catheter for 15 to 30 min before specimen collection. Cleanse specimen port with antiseptic swab, and then aspirate 5 mL of urine with a 21- to 25-gauge needle and syringe. Transfer urine to a sterile container.
  • Timed Specimen

  • Obtain a clean 3-L urine specimen container, toilet-mounted collection device, and plastic bag (for transport of the specimen container). The specimen must be refrigerated or kept on ice throughout the entire collection period. If an indwelling urinary catheter is in place, the drainage bag must be kept on ice.
  • Begin the test between 6 and 8 a.m. if possible. Collect first voiding and discard. Record the time the specimen was discarded as the beginning of the timed collection period. The next morning, ask the patient to void at the same time the collection was started and add this last voiding to the container. Urinary output should be recorded throughout the collection time.
  • If an indwelling catheter is in place, replace the tubing and container system at the start of the collection time. Keep the container system on ice during the collection period, or empty the urine into a larger container periodically during the collection period; monitor to ensure continued drainage, and conclude the test the next morning at the same hour the collection was begun.
  • At the conclusion of the test, comparethe quantity of urine with the urinary output record for the collection; if the specimen contains less than what was recorded as output, some urine may have been discarded, invalidating the test.
  • Include on the collection container’s label the amount of urine, test start and stop times, and ingestion of any foods or medications that can affect test results.
  • General

  • Promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Nutritional Considerations: Vitamin D is necessary for the body to absorb phosphorus. Educate the patient with vitamin D deficiency, as appropriate, that the main dietary sources of vitamin D are cod liver oil and fortified dairy foods such as milk, cheese, and orange juice. Explain to the patient that vitamin D is also synthesized by the body, in the skin, and is activated by sunlight.
  • Increased urine phosphorus levels may be associated with the formation of kidney stones. Educate the patient, if appropriate, on the importance of drinking a sufficient amount of water when kidney stones are suspected.
  • Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include ALP, calcitonin, calcium, calculus kidney stone panel, chloride, CT abdomen, cystoscopy, IVP, KUB studies, PTH, parathyroid scan, phosphorus blood, potassium, renogram, retrograde ureteropyelography, uric acid, and UA.
  • Refer to the Endocrine and Genitourinary systems tables at the end of the book for related tests by body system.
Handbook of Laboratory and Diagnostic Tests, © 2013 Farlex and Partners