C-reactive protein (CRP) is a protein associated with acute inflammation or infection. CRP increases up to 1000-fold at sites of infection or inflammation. CRP is commonly measured using enzyme-linked immunosorbent assays (ELISA), immunoturbidimetry or antibody-based nephelometric assays.
The protein can be found in the native CRP (nCRP) form as a homopentameric protein and also the monomeric CRP (mCRP) form. nCRP can irreversibly dissociate into five separate monomers of mCRP at sites of inflammation and infection. CRP is mainly synthesized in liver hepatocytes and also produced in muscle cells, macrophages, endothelial cells, lymphocytes and adipocytes. Hormone replacement therapy of estrogen affects CRP levels. CRP has roles in inflammatory processes and host responses to infection such as complement pathway, apoptosis, phagocytosis, nitric oxide (NO) release and production of cytokines. It is thought that each of the CRP isoforms, nCRP and mCRP, have distinct biological properties with nCRP showing more anti-inflammatory properties than mCRP. mCRP has been shown to promote chemotaxis and recruitment of circulating leuocytes to areas of inflammation and can delay apoptosis.
CRP can be used for early diagnosis of pneumonia. For COVID-19 disease caused by coronavirus SARS-CoV-2 CRP has been shown to have prognostic value for progression from mild to severe COVID-19. CRP levels have been positively correlated with lung lesion and COVID-19 disease severity.
C-reactive protein concentrations as a marker of inflammation or infection for interpreting biomarkers of micronutrient status
World Health Organization