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Refractive index of serum or plasma

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

This test measures how light bends through your blood serum or plasma, which can help assess hydration, protein levels, or other conditions affecting fluid density.

Quick summary

["Light bending in your blood may signal dehydration, protein changes, or other health concerns."]

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

Key facts at a glance

LOINC
14345-3
Short code
Sp Gr Amn Refractometry
Synonyms
Sp Gr Amn Refractometry
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
refractometry
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

What Does This Test Measure?

Refractometry measures the refractive index—a property of how light passes through a liquid—using a specialized device. This test indirectly reflects the concentration of solutes (like proteins, electrolytes, or glucose) in your serum or plasma. Lower refractive indices often suggest dehydration or lower solute levels, while higher values may indicate concentrated fluids or elevated proteins.

Why Might You Need This Test?

Your healthcare provider may order this test to evaluate hydration status, monitor conditions affecting blood composition (e.g., liver disease, kidney issues), or check for abnormalities in protein or electrolyte balance.

Common Uses and Conditions

This test is sometimes used in clinical settings to confirm or support diagnoses like dehydration, hyperproteinemia (high protein levels), or to monitor treatment responses in conditions like cirrhosis or kidney disease.

What to Expect Before the Test

No special preparation is needed. A blood sample is drawn from a vein, similar to other blood tests. If you’re dehydrated, your provider may advise drinking fluids beforehand.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: How This Test Helps Healthcare Providers

Short name

Serum/Plasma Refractometry

Frequently asked questions

How will my results affect my care?
Results help doctors assess whether your blood is too thin (diluted) or too thick (concentrated), which can guide treatment for hydration, infections, or metabolic issues. Abnormal results may prompt further testing for underlying causes.
What does a high or low refractive index mean?
A higher refractive index could suggest concentrated blood (e.g., dehydration, high protein levels), while a lower value may indicate diluted blood (e.g., overhydration, low protein). Your provider will interpret results in context with your symptoms and other tests.
Can this test detect specific diseases?
This test isn’t disease-specific but can signal broader trends in fluid or protein balance. It’s often used alongside other tests to support a diagnosis, such as dehydration or liver/kidney dysfunction.
  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