Understanding Your Diagnostic Test and Sample Collection

Published: July 31, 2026Updated: August 16, 2026

This test measures urea nitrogen levels in the vitreous fluid of the eye, primarily used in forensic pathology to assess kidney function.

Quick summary

{"Measures urea nitrogen in the clear fluid inside the eye","Mainly used in forensic investigations to determine kidney function at time of death","Helps estimate time of death and assess renal status","Not a routine test for living patients","Results must be interpreted by forensic pathologists"}

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

Key facts at a glance

LOINC: 17758-4
Short code: UN-Vitreous
Synonyms: Urea nit Vitf-mCnc
Category: chemistry
Sample: serum
Container: Sterile container for vitreous fluid collection; typically collected via trans-scleral aspiration from the eye
Units: not specified
Ref low: 8
Ref high: 25
Critical range: — – 100 not specified
Fasting: false
Population: adult
Sex: all
Age range: 18–65 years
Method: Enzymatic or Colorimetric
CPT: 84520
SNOMED: 271456004
Specimen volume: 0.5-1.0 mL of vitreous fluid
Stability: Refrigerated (2-8°C) for up to 72 hours; frozen (-20°C) for longer storage. Avoid repeated freeze-thaw cycles.
Hemolysis max: 500
Lipemia max: 1000
Icterus max: 500
TAT: 24–72 hours
Order: routine

What is this test, and what information can it provide about your health? This diagnostic test examines a patient sample to help your healthcare professional assess a medical condition, monitor treatment, or guide next steps in care.

The Vitreous Fluid Urea Nitrogen test measures the concentration of urea nitrogen in the vitreous humor—the clear, gel-like substance that fills the space between the lens and the retina of the eye. This test is primarily performed in forensic or post-mortem settings rather than as a routine clinical test for living patients.

How is the sample collected? Depending on the test, a trained healthcare professional may collect blood, urine, saliva, a swab, or another specimen using standard procedures designed to protect your comfort, privacy, and safety.

A small sample of vitreous fluid is collected from the eye using a fine needle during a post-mortem examination. The procedure is performed by a qualified forensic pathologist or medical examiner. This fluid is relatively isolated from the rest of the body and changes slowly after death, making it valuable for analysis.

Reference range

8-25 mg/dLnot specified

Specimen: serum

No special preparation; typically postmortem specimen

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

In forensic medicine, vitreous fluid urea nitrogen levels help assess kidney function at or near the time of death. Elevated levels may indicate renal failure, dehydration, or other conditions affecting kidney function prior to death. This information can assist in determining cause of death and estimating post-mortem interval. Additionally, comparing vitreous urea nitrogen with blood urea nitrogen levels can provide insights into the deceased's medical history and terminal condition.

Frequently asked questions

Why is vitreous fluid tested instead of blood?

Vitreous fluid is relatively protected from decomposition and contamination that affects blood samples after death. It remains stable longer and provides a more reliable indicator of the body's metabolic state at the time of death.

Is this test painful?

This test is performed after death, so there is no pain involved. It is part of a forensic autopsy procedure conducted by trained professionals.

What do high urea nitrogen levels mean?

Elevated vitreous urea nitrogen may indicate pre-existing kidney disease, acute renal failure, dehydration, or other conditions that affected kidney function before death. Interpretation requires correlation with other autopsy findings.

Can this test be done on living patients?

This specific test on vitreous fluid is not routinely performed on living patients. It is primarily a forensic tool. For living patients, blood or urine tests are used to measure urea nitrogen levels.

Sources

1
LOINC Code ReferenceSource
2
Forensic Pathology: A Handbook of MethodsSource

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