C-reactive protein (CRP) by nephelometry
This test measures the level of C-reactive protein, a protein produced by the liver in response to inflammation in your body.
["CRP helps identify inflammation, often used to monitor conditions like infections or autoimmune diseases."]
Key facts at a glance
- LOINC
- 78384-5
- Short code
- CATD1
- Synonyms
- Cat dander (nFel d) 1 IgE Qn
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or red-top tube
- Units
- N/A
- Ref low
- 0
- Ref high
- 0.34
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- Immunoassay (Fluorescent Enzyme Immunoassay or Chemiluminescent Immunoassay)
- CPT
- 86003
- SNOMED
- 395147008
- Specimen volume
- 1.0 mL serum (minimum 0.5 mL)
- Stability
- Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30 days
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 24–72 hours
- Order
- routine
Why Is This Test Done?
Your healthcare provider may order this test to check for signs of inflammation, monitor chronic conditions like rheumatoid arthritis or lupus, or evaluate responses to treatments. It can also be used to assess risk for heart disease or infection.
What to Expect Before the Test
No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if it’s a fasting CRP, but this is less common for standard CRP measurements. Bring any medications you’re currently taking.
How the Test Works
A small blood sample is drawn from a vein, typically in your arm. The sample is analyzed in a lab using nephelometry, a method that measures how much light scatters when CRP binds to antibodies.
What the Results Mean
Results are typically reported in milligrams per liter (mg/L). Higher levels may indicate inflammation, infection, or other underlying health issues. Your provider will interpret the results in the context of your medical history and symptoms.
Reference range
Class 0: <0.35 kU/L (Negative); Class 1: 0.35-0.69 kU/L (Low); Class 2: 0.70-3.49 kU/L (Moderate); Class 3: 3.50-17.49 kU/L (High); Class 4: 17.50-49.99 kU/L (Very High); Class 5: 50.00-99.99 kU/L (Very High); Class 6: >=100.00 kU/L (Very High)N/A
No special preparation required. Patient should inform provider of current antihistamine or corticosteroid use, though these typically do not affect IgE antibody levels.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: CRP’s Role in Health
Short name
CRP (Nephelometry)
Frequently asked questions
What causes elevated CRP levels?
What does a normal CRP level indicate?
Can CRP levels change over time?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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