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Osmolarity of urine (24-hour collection)

Published: August 9, 2026Updated: August 16, 2026

This test measures the concentration of dissolved substances in your urine over a 24-hour period, helping assess how well your kidneys are balancing water and electrolytes.

Quick summary

["Helps diagnose kidney function and fluid balance issues."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
79811-6
Short code
Study obs Ocul fund-R Angio W indocy gr
Synonyms
Study obs Ocul fund-R Angio W indocy gr
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
angiography
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your doctor may order this test if you have symptoms like frequent urination, dehydration, kidney problems, or conditions affecting fluid balance (e.g., diabetes, heart failure). It can also be part of routine checks for kidney health or to evaluate responses to medications that affect fluid retention.

What to Expect Before the Test

You’ll collect all urine for 24 hours in a special container. Drink enough fluids to produce urine consistently, but avoid excessive intake. Follow your doctor’s instructions carefully to ensure accurate results.

How the Test Works

The collected urine is analyzed in a lab to measure the total concentration of solutes (like sodium, glucose, and waste products) dissolved in the urine. This helps determine how concentrated or dilute your urine is.

What the Results Mean

Higher than expected osmolarity may indicate dehydration, kidney disease, or conditions that restrict urine production. Lower values could suggest overhydration or kidney dysfunction that allows more water to pass through urine.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Urine Osmolarity

Frequently asked questions

What causes abnormal urine osmolarity?
Abnormal urine osmolarity can result from dehydration (too low), kidney disease (too high or low), diabetes insipidus (extremely low), or excessive fluid intake (too low). Always discuss symptoms with your doctor.
How often should I get this test?
Your doctor will determine frequency based on your health needs—this may include routine checks, monitoring chronic conditions, or evaluating symptoms like thirst, fatigue, or changes in urine appearance.
Can I drink alcohol before this test?
Avoid excessive alcohol before the test, as it may affect fluid balance and urine concentration. Stick to your usual fluid intake unless instructed otherwise.
  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 16, 2026. · Read our editorial policy