CRP is used mainly as an inflammation marker. Apart from liver failure, there are few known factors that interfere with CRP production. Interferon alpha inhibits CRP production from liver cells which may explain the relatively low levels of CRP found during viral infections compared to bacterial infections 
Measuring and charting CRP values can prove useful in determining disease progress or the effectiveness of treatments. ELISA, immunoturbidimetry, nephelometry, radial immunodiffusion
* low: hs-CRP level under 1.0 mg/L
* average: between 1.0 and 3.0 mg/L
* high: above 3.0 mg/L
Normal levels increase with aging. Higher levels are found in late pregnant women, mild inflammation and viral infections (10–40 mg/L), active inflammation, bacterial infection (40–200 mg/L), severe bacterial infections and burns (>200 mg/L).
CRP cut-off levels indicating bacterial from non-bacterial illness can vary due to co-morbidities such as malaria, HIV and malnutrition and the stage of disease presentation.
CRP is a more sensitive and accurate reflection of the acute phase response than the ESR (erythrocyte sedimentation rate). ESR may be normal while CRP is elevated. CRP returns to normal more quickly than ESR in response to therapy.