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24-Hour Urine Phosphate-to-Creatinine Ratio

Published: August 9, 2026Updated: August 17, 2026

Measures phosphate relative to creatinine in urine collected for 24 hours to help evaluate the body's phosphate balance and kidney handling.

Quick summary

["This test can help identify abnormal phosphate loss in the urine and guide evaluation of conditions that affect phosphate levels."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
56965-7
Short code
Phosphate/Creat 24h Ur-Rto
Synonyms
Phosphate/Creat 24h Ur-Rto
Category
kidney
Sample
urine
Container
Sterile urine container
Units
N/A
Ref low
2.5
Ref high
4.5
Critical range
1 N/A – —
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84100
Specimen volume
10 mL
Stability
Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

What is this test?

This test measures the amount of phosphate in a 24-hour urine collection and compares it with the amount of creatinine. Creatinine is used as a marker of how much urine was produced.

Why might I need this test?

A clinician may order it when blood phosphate levels are unexpectedly low or high, or when evaluating disorders that affect kidney phosphate handling, vitamin D regulation, or parathyroid hormone.

How is the test performed?

You collect all urine for a full 24-hour period, usually in a labeled container provided by the laboratory. The laboratory measures phosphate and creatinine and calculates their ratio.

How do I prepare for the test?

Follow the laboratory's collection instructions and record the start and finish times. Collect every urine sample during the 24-hour period and keep the container refrigerated if instructed. Do not change your diet or medications unless your clinician tells you to do so.

Reference range

Adult: 2.5-4.5 mg/dLN/A

Specimen: urine

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

24-Hour Urine Phosphate/Creatinine Ratio

Frequently asked questions

Why is urine collected for 24 hours?
A 24-hour collection captures the total amount of phosphate and creatinine excreted during a full day, providing a more complete assessment than a single urine sample.
Does the test use blood or urine?
This test uses urine collected for 24 hours. Your clinician may also order blood phosphate and kidney function tests for comparison.
What if I miss part of the urine collection?
Tell the laboratory or your clinician, because an incomplete collection can make the result less reliable. The collection may need to be repeated.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy