Normal Range for C-Reactive Protein (CRP)
The normal range for C-Reactive Protein (CRP) is typically below 3 mg/L in healthy individuals, with values above 10 mg/L strongly suggesting an active inflammatory or infectious process. 1, 2, 3
Standard CRP Reference Ranges
- CRP concentrations in healthy individuals are typically below 3 mg/L 1, 2
- The American Heart Association and CDC recommend categorizing cardiovascular risk based on CRP levels as: 1
- Low risk: <1.0 mg/L
- Average risk: 1.0-3.0 mg/L
- High risk: >3.0 mg/L
- Values above 10 mg/L have traditionally been considered indicative of acute inflammation or infection 1
- If CRP level is ≥10 mg/L, the test should be repeated and the patient examined for sources of infection or inflammation 1
Interpretation of Elevated CRP Values
- Moderate elevation (3-10 mg/L) may indicate chronic low-grade inflammation 3
- Different conditions show varying degrees of CRP elevation: 1, 2
- Bacterial infections: median ~120 mg/L
- Inflammatory diseases: median ~65 mg/L
- Solid tumors: median ~46 mg/L
- Non-bacterial infections: median ~32 mg/L
- Cardiovascular disease: median ~6 mg/L
- CRP rises 4-6 hours after an inflammatory trigger and peaks at 36-50 hours 4
Factors Affecting CRP Levels
- Non-pathological factors that can influence CRP levels include: 1, 3
- Age, sex, and race
- Body mass index and obesity
- Smoking (approximately 20% of smokers have CRP >10 mg/L)
- Socioeconomic status
- Exercise, diet, and sleep patterns
- Medication use
Clinical Applications
- For cardiovascular risk assessment, high-sensitivity CRP (hsCRP) assays are used to detect concentrations down to 0.3 mg/L 1
- In neonatal sepsis evaluation, two CRP measurements 24 hours apart that are <10 mg/L are useful in excluding sepsis 4
- CRP values that fail to decrease or continue to rise after 48 hours of antibiotic therapy suggest treatment failure 4
- When evaluating for bacterial vs. viral infections, a CRP value of 40 mg/L has better specificity (0.88) than lower cutoffs for distinguishing bacterial from viral respiratory infections 5
Important Considerations
- A single CRP measurement is neither sensitive nor specific enough to identify all patients with serious bacterial infection 4
- The acute phase response can be triggered at very low inflammatory levels with CRP values considerably lower than 5-10 mg/L 6
- Population distributions of CRP have changed over time, with 30-40% of US adults now exhibiting CRP levels >3 mg/L 1
- For research purposes, automatically excluding all values >10 mg/L may inadvertently exclude individuals with chronic inflammation of interest 1