Skip to main content
DNA Labs India

Osmolal Gap Serum Test

DNA Labs India | ISO 9001:2015 Certified

Osmolal Gap Serum Test

Short Name: Osmolal Gap Serum

Also known as: Osmolal Gap Test, Osmolar Gap Serum, Serum Osmolal Gap

Osmolal Gap Serum Test test available at DNA Labs India for ₹1,147. Uses Freezing Point Depression, Spectrophotometry, Calculated on Serum and Plasma samples. Results in Reports are generally available on the same day if the sample is received by 4 pm.. Free home collection in 300+ cities across India.

BiochemistryAll 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 purpose of this test is to detect unmeasured osmotically active substances by comparing measured and calculated serum osmolality. It aids in identifying toxic alcohols, ketoacids, and other osmolar disturbances. It is used alongside blood gas, electrolytes, BUN, and glucose.

Test Code
3514
Price
₹1,147
Sample Type
Serum and Plasma
Result Time
Reports are generally available on the same day if the sample is received by 4 pm.
Fasting Required
No
Method
Freezing Point Depression, Spectrophotometry, Calculated
Step 1

Sample Collection

No special preparation is required. Fasting is not needed.

Method: Venipuncture

Step 2

Laboratory Analysis

A tourniquet may be applied; blood is drawn from a vein into an SST and a grey top tube.

Step 3

Report Delivery

Apply pressure at the puncture site; normal activities can generally be resumed.

Timeline: Reports are generally available on the same day if the sample is received by 4 pm.

Patient Instructions

1
Before the Test:No special preparation or fasting is required before the test.
2
During the Test:Blood is collected from a vein into an SST and a grey top sodium fluoride tube.
3
After the Test:Keep the puncture site clean and apply pressure if mild bleeding occurs.

About This Test

Who Should Get This Test

The purpose of this test is to detect unmeasured osmotically active substances by comparing measured and calculated serum osmolality. It aids in identifying toxic alcohols, ketoacids, and other osmolar disturbances. It is used alongside blood gas, electrolytes, BUN, and glucose.

How to Prepare

  • No special preparation required.
  • Inform the phlebotomist about recent medications or alcohol exposure.
  • Serum and plasma samples should be separated within 1 hour of collection.

Doctor's Notes

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

"The osmolal gap helps identify unmeasured osmotically active substances in acute settings. If the gap is raised, consider toxic alcohol exposure or ketoacidosis and order specific toxicology assays when clinically indicated."

Last medically reviewed: September 7, 2026

Test Parameters & Specifications

Sample TypeSerum and Plasma
Sample VolumeSerum: 3 mL (1.5 mL min.); Plasma: 2 mL (1 mL min.)
ContainerSST (Serum Separator Tube) and Grey Top (Sodium Fluoride) tube
Collection MethodVenipuncture

Sample Stability

Room temperature: 3 hours
Refrigerated: 72 hours
Frozen: 1 week
Separate serum and plasma within 1 hour of collection
Sample Rejection Criteria:
  • Grossly hemolysed samples
  • Improperly labeled or unseparated samples
  • Quantity insufficient for analysis

Understanding Your Results

The osmolal gap is interpreted by comparing measured serum osmolality with calculated osmolality. Reference values may vary slightly between laboratories.
📊

Suggests unmeasured osmotically active substances such as ethanol, methanol, ethylene glycol, mannitol, or ketoacids.

📊

May indicate electrolyte or water imbalance; correlate with sodium and clinical status.

📊

Generally considered normal, but clinical correlation remains essential.

⚠️ When to Consult a Doctor:

Consult a doctor if you have confusion, disorientation, dizziness, seizures, nausea, vomiting, fatigue, weakness, increased thirst, dry mouth, or suspected toxic ingestion.

Limitations

  • ⚠Osmolal gap does not identify the exact toxic alcohol; specific assays are needed.
  • ⚠A normal osmolal gap does not completely exclude early toxic alcohol ingestion.
  • ⚠Results must be interpreted with clinical findings and other laboratory tests.

Risks & Considerations

  • ●Minor bruising at the venipuncture site
  • ●Mild bleeding
  • ●Lightheadedness
  • ●Infection at puncture site is rare

Interfering Factors

  • ●Gross hemolysis
  • ●Delayed separation of serum and plasma
  • ●Lipemic samples
  • ●Recent alcohol or mannitol administration
  • ●Incorrect calculated osmolality inputs

Compare With Similar Tests

TestOsmolal Gap Serum Test
ComparisonOsmolal Gap Serum Test

Frequently Asked Questions

What is the Osmolal Gap Serum Test?
It measures the difference between measured serum osmolality and calculated serum osmolality to detect unmeasured osmotically active substances.
Why is this test done?
It helps evaluate suspected toxic alcohol ingestion, alcohol intoxication, diabetic ketoacidosis, drug overdose, and electrolyte disturbances.
Is fasting required for the test?
No, fasting is not required. No special preparation is needed.
What sample is required?
Serum from an SST and plasma from a grey top sodium fluoride tube are required, separated within 1 hour of collection.
How is calculated osmolality determined?
It is derived from serum sodium, glucose, and blood urea nitrogen concentrations.
What does a high osmolal gap indicate?
It suggests unmeasured osmoles such as ethanol, methanol, ethylene glycol, mannitol, or ketoacids.
What does a low osmolal gap indicate?
It may suggest electrolyte or water imbalance and should be correlated with sodium and clinical findings.
What is the cost of this test?
The test costs Rs 1146.6 at DNA Labs India.
Is home sample collection available?
Yes, free home sample collection is available for online bookings across many Indian cities.
When will the report be available?
Reports are generally available on the same day if the sample reaches the laboratory by 4 pm.
What symptoms may indicate the need for this test?
Confusion, dizziness, fatigue, weakness, increased thirst, dry mouth, nausea, vomiting, or seizures.
Can the osmolal gap identify the exact toxic substance?
No, it detects the presence of unmeasured osmoles; specific assays are needed to identify particular toxins.
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.

Related Tests

Amino Acid Non-Ketotic Hyperglycinemia Panel Quantitative CSF & Plasma Test

₹9,000

Amino Acids Maple Syrup Urine Disease (MSUD) Panel Plasma Test

₹6,000

Amino Acids Quantitative Urine: 45 Amino Acids / Full Panel Test

₹7,500

Amino Acids Quantitative Urine & Plasma: 45 Amino Acids / Full Panel Test

₹11,000

Porphobilinogen (PBG) Quantitative 24 Hour Urine Test

₹5,000

Purkinje Cell Cytoplasmic Antibody Type Tr (DNER) Test

₹4,500
For Hospitals & Clinics

Reference Laboratory Services

We serve as a reference laboratory for hospitals and clinics across India. Send samples from your facility with same-day pickup, priority processing, and results delivered through our online portal. Competitive institutional pricing available.

LIMS Integration

Your Data Privacy

Your medical data is protected under Indian law.

✓ Stored in India: All patient records are stored on servers located in India. No data is transferred outside the country.

✓ DPDP Act Compliant: Under the Digital Personal Data Protection Act 2023, you can request deletion of your records at any time by contacting support.

Book Your Test

Enter your details and we'll connect you within 15 minutes.

🧬

Quick Connect

Enter your mobile number and we’ll connect you with the team.

+91

✅ Connecting you now...

🔒 Your number is used to respond to this request.