diagnostics
CRP Test: What Is C-Reactive Protein and When Should You Get It?
By Dashvanth Healthcare Medical Team · Reviewed by our specialists · East Delhi
What Is CRP?
C-Reactive Protein (CRP) is an acute-phase protein produced by the liver in response to inflammation. It rises sharply within 6–8 hours of tissue injury or infection, making it a sensitive and rapid marker of inflammation.
Two Types of CRP Tests
Standard CRP
- Normal: <10 mg/L
- Used to detect significant inflammation or infection
- Very sensitive to acute infection — 50–500 mg/L in bacterial infection
High-Sensitivity CRP (hs-CRP)
- Measures much lower CRP levels (0.5–10 mg/L)
- Used for CARDIOVASCULAR RISK stratification (not acute infection)
- Low risk: <1 mg/L; Average risk: 1–3 mg/L; High risk: >3 mg/L
- hs-CRP >3 mg/L doubles cardiovascular event risk independent of cholesterol
What Elevated CRP Tells You
| CRP Level | Likely Significance |
|---|---|
| <1 mg/L | Normal / Low CV risk |
| 1–10 mg/L | Mild inflammation, viral infection, autoimmune flare |
| 10–40 mg/L | Moderate infection or inflammation |
| >40 mg/L | Significant bacterial infection |
| >100 mg/L | Severe bacterial infection, sepsis |
CRP vs ESR: Which Is Better?
- CRP rises faster (6–8 hours) and normalises faster (after treatment)
- ESR rises slower and remains elevated longer — less useful for acute monitoring
- CRP preferred for monitoring treatment response; ESR for chronic conditions (vasculitis, polymyalgia)
Can CRP distinguish bacterial from viral infection?
Generally yes — bacterial infections cause CRP >80–100 mg/L; viral infections rarely exceed 40 mg/L. However, there is significant overlap. CRP is most useful when interpreted alongside clinical findings, WBC differential and procalcitonin.
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