CRP Test
Also known as: C-Reactive Protein
What is CRP?
CRP (C-reactive protein) is a substance produced by the liver in response to inflammation. It is a marker of acute inflammation and infection.[MedlinePlus (NIH)]
What This Test Measures
This test measures the level of CRP in your blood. Elevated levels indicate inflammation somewhere in the body.[Mayo Clinic]
Why It's Important
CRP helps detect and monitor inflammation from infections, autoimmune diseases, and other conditions.[MedlinePlus (NIH)]
CRP rises quickly with inflammation and falls as inflammation resolves, making it useful for monitoring treatment.[Cleveland Clinic]
Who Should Get This Test?
CRP is ordered to detect and monitor acute inflammation from various causes.
Risk Factors
- Symptoms of infection (fever, chills, malaise)
- Suspected autoimmune disease (lupus, rheumatoid arthritis)
- Post-surgical monitoring for infection
- Monitoring inflammatory conditions
- Unexplained fever or inflammation
- Sepsis evaluation
- Assessing response to antibiotic therapy
- Flare-ups of chronic inflammatory conditions
Screening Schedule
Ordered when infection or inflammation is suspected; repeated to monitor treatment response or disease activity.
What Happens During the Test
A blood sample is drawn from a vein. CRP is measured using immunoturbidimetric or immunonephelometric assays. No fasting required.
Duration
5-10 minutes for blood draw; results often available within hours
Discomfort Level
Minimal discomfort from needle insertion
Risks & Side Effects
Standard blood draw with minimal risks.
- •Brief pain at needle site
- •Small bruise may develop
- •Rare: lightheadedness
- •Very rare: infection at puncture site
Normal Range
Less than 10 mg/L. Most healthy people have levels below 3 mg/L.
Note: Levels can rise dramatically (100+ mg/L) during acute infections.
Source: MedlinePlus (NIH)Unit Conversion
Convert between mg/L and mg/dL
| mg/L | mg/dL |
|---|---|
| 3 | 0.3 |
| 10 | 1 |
| 50 | 5 |
| 100 | 10 |
| 200 | 20 |
High Values
High CRP indicates inflammation from infection, autoimmune disease, tissue injury, or cancer. Very high levels suggest serious bacterial infection.[Mayo Clinic]
Low Values
Low CRP is normal and indicates absence of significant inflammation.[Cleveland Clinic]
Test Limitations & Accuracy
CRP interpretation has several considerations:
- ⚠CRP is nonspecific - elevated in many conditions without indicating the cause
- ⚠Recent injury, surgery, or trauma can elevate CRP
- ⚠Obesity and smoking cause mild chronic CRP elevation
- ⚠Cannot distinguish between bacterial and viral infections reliably
- ⚠Normal CRP does not rule out all infections
- ⚠Some medications (statins, NSAIDs) can lower CRP
- ⚠Pregnancy can affect CRP levels
Alternative & Complementary Tests
CRP is often ordered with other markers to evaluate inflammation:
For cardiovascular risk assessment (measures lower levels)
Another marker of inflammation; rises and falls more slowly than CRP
More specific for bacterial infections and sepsis
WBC count also indicates infection/inflammation
Acute phase reactant that rises with inflammation
References
Medical Disclaimer
This information is for educational purposes only and is not intended as medical advice. Always consult with a qualified healthcare provider for interpretation of test results and medical decisions.
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