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Osmolality Urine : Serum Ratio Test

DNA Labs India | ISO 9001:2015 Certified

Osmolality Urine : Serum Ratio Test

Short Name: Osmolality Urine : Serum Ratio

Also known as: Urine Osmolality to Serum Osmolality Ratio, U Osmolality: Serum Osmolality Ratio, Osmolality Urine/Serum Ratio, Urine-Serum Osmolality Ratio

Osmolality Urine : Serum Ratio Test test available at DNA Labs India for ₹1,451. Uses Freezing Point Depression on 2 mL (1.5 mL min.) serum from 1 SST AND 5 mL (3 mL min.) aliquot of random urine samples. Results in Reports are generally available the same day when samples are collected by 3 pm.. Free home collection in 300+ cities across India.

Renal Function TestAll Age Groups🏠 Home Collection

✍️ Written By

🩺 Medically Reviewed By

Dr Ramarao Paidisetty

Dr Ramarao Paidisetty

Consultant Biochemist · Reg: 21504

Last reviewed: September 7, 2026

Overview

The test measures the ratio of urine osmolality to serum osmolality to evaluate the kidney's ability to concentrate or dilute urine and to help diagnose and monitor dehydration, kidney diseases, and disorders of water balance such as diabetes insipidus.

Test Code
3515
Price
₹1,451
Sample Type
2 mL (1.5 mL min.) serum from 1 SST AND 5 mL (3 mL min.) aliquot of random urine
Result Time
Reports are generally available the same day when samples are collected by 3 pm.
Fasting Required
No
Method
Freezing Point Depression
Step 1

Sample Collection

No special preparation is required. Inform the collection team of any ongoing diuretic or fluid therapy.

Method: Venepuncture for serum; random urine collection

Step 2

Laboratory Analysis

A blood sample is collected from a vein into an SST tube, and a random urine sample is collected in a sterile container without preservative.

Step 3

Report Delivery

Resume normal activities. Mild bruising at the venepuncture site may occur.

Timeline: Reports are generally available the same day when samples are collected by 3 pm.

Patient Instructions

1
Before the Test:No special preparation required
2
During the Test:A paired blood sample and random urine sample are collected
3
After the Test:Resume normal activities

About This Test

Who Should Get This Test

The test measures the ratio of urine osmolality to serum osmolality to evaluate the kidney's ability to concentrate or dilute urine and to help diagnose and monitor dehydration, kidney diseases, and disorders of water balance such as diabetes insipidus.

How to Prepare

  • Do not use preservative in the urine container
  • Separate serum within 1 hour of collection
  • Ship refrigerated
  • Do not freeze the samples

Doctor's Notes

Reviewed by — MBBS, MD (Biochemistry) · Reg. No. 21504

"The urine to serum osmolality ratio helps differentiate prerenal azotemia from intrinsic renal disease and is useful in evaluating polyuria when interpreted with hydration status."

Last medically reviewed: September 7, 2026

Test Parameters & Specifications

Sample Type2 mL (1.5 mL min.) serum from 1 SST AND 5 mL (3 mL min.) aliquot of random urine
Sample Volume2 mL serum and 5 mL random urine
ContainerSST tube for serum; sterile urine container
Collection MethodVenepuncture for serum; random urine collection

Sample Stability

Room temperature: NA
Refrigerator: 72 hours
Frozen: NA

Understanding Your Results

The urine to serum osmolality ratio compares the concentration of urine with that of serum. A ratio greater than 1 indicates urine is more concentrated than serum, while a ratio less than 1 indicates dilute urine. The ratio should be interpreted alongside the clinical picture, serum sodium, and urine output.
📊

Ratio >1

Urine is concentrated relative to serum; may indicate normal renal concentrating ability or prerenal state.

📊

Ratio <1

Urine is dilute relative to serum; may be seen in diabetes insipidus, excessive water intake, or impaired renal concentrating ability.

📊

Ratio near 1

Iso-osmotic urine; may suggest intrinsic renal disease with fixed osmolality.

⚠️ When to Consult a Doctor:

Consult a physician or nephrologist if the test is abnormal, or if you experience excessive thirst, frequent urination, dizziness, fatigue, dark urine, or signs of dehydration.

Limitations

  • ⚠A single random ratio must be interpreted with hydration status and serum sodium
  • ⚠It does not replace a water deprivation test when indicated
  • ⚠Urine and serum must be collected at the same time for accurate ratio

Risks & Considerations

  • ●Mild pain or bruising at the venepuncture site

Interfering Factors

  • ●Recent intravenous contrast or mannitol
  • ●Diuretic use
  • ●Ethanol ingestion
  • ●Hydration status at the time of collection
  • ●Hyperglycaemia or uraemia

Compare With Similar Tests

TestOsmolality Urine : Serum Ratio Test
ComparisonOsmolality Urine : Serum Ratio Test

Frequently Asked Questions

What is the Osmolality Urine : Serum Ratio Test?
It is a medical test that measures the concentration of dissolved particles in urine and serum and calculates the ratio of urine osmolality to serum osmolality.
Why is the test done?
It is used to diagnose and monitor kidney diseases, dehydration, diabetes insipidus, and other conditions affecting water balance.
Is fasting required for this test?
No special preparation or fasting is required.
What sample is needed?
A 2 mL serum sample from an SST tube and a 5 mL random urine sample without preservative are required.
How is the test performed?
A blood sample is drawn from a vein and a random urine sample is collected at the same time. Both are analysed by freezing point depression.
What is the cost of the Osmolality Urine : Serum Ratio Test in India?
At DNA Labs India, the test costs Rs 1450.8.
What is the normal serum osmolality?
The usual reference range for serum osmolality is 275-295 mOsm/kg H2O.
What does a high urine to serum osmolality ratio mean?
A ratio greater than 1 means urine is concentrated relative to serum, which may indicate normal renal concentrating ability or a prerenal state.
What does a low urine to serum osmolality ratio mean?
A ratio less than 1 means urine is dilute relative to serum, which may be seen in diabetes insipidus, excessive water intake, or impaired concentrating ability.
How long does it take to get the report?
Reports are generally available the same day if the sample reaches the laboratory by 3 pm.
Is home sample collection available?
Yes, DNA Labs India offers free home sample collection for online bookings for this test across available cities.
Which doctor should I consult if my result is abnormal?
You should consult a physician or nephrologist, especially if you have symptoms such as excessive thirst, frequent urination, fatigue, or dizziness.
Worried about the process? Our certified phlebotomists collect thousands of samples every month across India. The process takes under 5 minutes and is virtually painless. Questions? Message us on WhatsApp — we're here 7 days a week.

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