This is an acute phase protein, normally present in the plasma at a concentration of less than 5 mg/l.
CRP increases in virtually all conditions associated with tissue damage and may double its concentration every 6 hours. The name derives from its ability to react with the C polysaccharide of Streptococcus pneumoniae, but it may also bind to chromatin in nuclear DNA-histone complexes. Once bound, it is able to activate the classical complement pathway.
CRP is better than ESR for monitoring fast changes as it does not depend on fibrinogen or immunoglobulin levels, and is not affected by red blood cell numbers and shape.
Uses of CRP include:
- screening for organic disease
- monitoring disease activity in conditions such as rheumatoid arthritis, infections or malignancy
- as a prognostic marker for conditions such as acute pancreatitis
- to distinguish bacterial from viral infections - more marked response to acute bacterial infection