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Ureanitplrmcnc

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

This test measures the amount of urea nitrogen in the fluid surrounding your lungs to help diagnose the cause of fluid buildup.

Quick summary

{"Measures urea nitrogen levels in fluid between the lungs and chest wall","Helps doctors determine why fluid has accumulated in the pleural space","Used to distinguish between different types of pleural effusions","A simple fluid sample collected during a procedure called thoracentesis","Results help guide treatment decisions for lung and chest conditions"}

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

Key facts at a glance

LOINC
14394-1
Short code
PLEURAL BUN
Synonyms
Urea nit Plr-mCnc
Category
chemistry
Sample
fluid
Container
Sterile screw-cap container (red-top, gray-top, or plain sterile container acceptable); avoid heparinized tubes as they may interfere with some assay methods
Units
not specified
Ref low
6
Ref high
24
Critical range
— – 100 not specified
Fasting
false
Population
adult
Sex
all
Age range
≥ 0 years
Method
Enzymatic or colorimetric method (urease-based reaction), similar to serum urea nitrogen determination
CPT
86356 (Miscellaneous body fluid analysis) or 82069 (Urea nitrogen, quantitative)
SNOMED
258268004
Specimen volume
1-5 mL of pleural fluid minimum; 2-5 mL preferred for optimal testing
Stability
Room temperature: 24-48 hours; Refrigerated (2-8°C): 72 hours; Avoid freezing. Analyze promptly for most accurate results. Centrifuge if specimen is viscous.
Hemolysis max
50
Lipemia max
100
Icterus max
20
TAT
2–24 hours
Order
routine

What is this test?

The pleural fluid urea nitrogen test measures the amount of urea nitrogen in the fluid that collects in the pleural space—the area between your lungs and the inner surface of your chest wall. Urea nitrogen is a waste product that your kidneys normally filter from your blood. This test helps doctors understand why fluid has built up in this area and what may be causing it.

How is the sample collected?

A healthcare provider will collect the pleural fluid sample using a procedure called thoracentesis. During this procedure, you will sit upright and lean forward on a table. The doctor will clean an area on your back, inject a local anesthetic to numb the area, and then insert a thin needle between your ribs to withdraw the excess fluid. The procedure usually takes 15-30 minutes. You may feel some pressure or discomfort during the needle insertion.

What do the results mean?

Your doctor will compare the urea nitrogen level in your pleural fluid with the level in your blood. This comparison helps determine the source of the pleural fluid and the likely cause of the effusion. The results, combined with other tests on the pleural fluid (such as protein, glucose, and cell counts), help doctors classify the effusion as either a transudate or an exudate, which guides treatment decisions.

Are there any risks?

Thoracentesis is generally safe, but like any procedure, it carries some risks. These may include bleeding, infection, pneumothorax (collapsed lung), or re-accumulation of fluid. Your healthcare team will monitor you closely and take precautions to minimize these risks. Contact your doctor immediately if you experience difficulty breathing, chest pain, or fever after the procedure.

Reference range

6-24 mg/dL (comparable to serum)not specified

Specimen: fluid

No special preparation required; specimen obtained by thoracentesis

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Frequently asked questions

Why do I need this test?
Your doctor has likely discovered fluid around your lungs through an X-ray, CT scan, or ultrasound. This test helps determine why that fluid accumulated, which is essential for choosing the right treatment. It provides clues about whether the fluid is due to a systemic condition affecting your whole body or a local problem in your chest.
How long does it take to get results?
Results are typically available within 1-3 days, depending on the laboratory. Your doctor will discuss the results with you at your follow-up appointment and explain what they mean for your specific condition.
Do I need to fast before this test?
No fasting is required for this test. However, your doctor may have ordered other blood tests alongside this one that might require fasting. Follow any specific instructions your healthcare provider gives you.
What happens after the fluid is removed?
Removing the pleural fluid often provides immediate relief from symptoms like shortness of breath. The fluid may be sent to a laboratory for analysis, and your doctor will discuss treatment options based on the results. In some cases, the fluid may reaccumulate, and additional procedures may be needed.
  1. 1
    Mayo Clinic - Pleural effusionSource
  2. 2
    MedlinePlus - ThoracentesisSource

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