About C-reactive protein (CRP)

About C-reactive protein (CRP)

C-reactive protein is a widely used diagnostic marker to aid evaluation of acute infections and inflammation, and to guide antibiotic treatment decisions.

What is C-reactive protein (CRP)?

C-reactive protein (CRP) is an extensively studied and widely used analyte in healthcare. CRP measurement aids in the diagnosis, evaluation, and monitoring of infection, tissue injury, inflammatory disorders, and associated diseases. CRP is an acute-phase plasma protein present in healthy individuals at low concentrations. The median CRP level of healthy people is usually < 0.8 mg/l and the reference value for CRP is < 3 mg/l1. However, each laboratory is recommended to establish the reference value for their population in the region.

Bacterial infections and inflammatory conditions stimulate the production of CRP in the liver. From the initial stimulus, CRP levels become detectable in 4-6 hours and peak in 36-48 hours2,3. In turn, when the infection or inflammation settles, CRP levels decrease rapidly back to normal with a half-life of 19h1,2.

CRP aids in the evaluation of disease severity and efficacy of antibiotic therapy

CRP production is proportional to the intensity of infection and inflammation4. Therefore, it is useful in the differentiation of mild and severe infections. If CRP level is < 10 mg/l, bacterial infection is unlikely5. In severe systemic bacterial infections, CRP may increase up to hundreds of mg/l. Viral and mild/self-limiting bacterial infections cause only a minor elevation or not elevation at all. Also, in the inflammatory diseases, CRP levels follow the severity of inflammation and may increase to moderate level, usually being between 10-40 mg/l.

CRP levels decrease rapidly as a response to treatment and infection resolution, making it a valuable tool to monitor the effectiveness of antibiotic treatment and disease progression. If CRP level does not decline within days after initiation of antibiotic therapy, it may be a sign of complicated disease or suggest ineffective antibiotic treatment6.

CRP point of care testing aids management of acute infections and guides antibiotic prescribing

Accurate, precise, and fast CRP point of care (POC) testing aids in the clinical management of patients with acute infection and optimises antibiotic prescribing. A small sample volume and immediate results due to the short analytical time offer a substantial benefit compared to a laboratory CRP test. When used together with the clinical examination of a patient, QuikRead go CRP tests are excellent tools in the following situations:

  • differentiating mild and severe infections4
  • increasing diagnostic confidence and guiding appropriate antibiotic prescribing in acute infections7,8
  • evaluation, monitoring, and prediction of the infection course, inflammation and treatment response6-9
  • ruling out severe bacterial infection10,11


  1. Shine, B et al. Solid phase radioimmunoassays for C-reactive protein. Clin. Chim. Acta 1981; 117:13–23.
  2. Vigushin DM, Pepys MB, Hawkins PN. Metabolic and scintigraphic studies of radioiodinated human C-reactive protein in health and disease. J Clin Invest 1993; 91(4): 1351-1357.
  3. Pepys MB, Hirschfield GM. C-reactive protein: a critical update. J Clin Invest 2003; 111(12): 1805-1812.
  4. Markanday A. Acute Phase Reactants in Infections: Evidence-Based Review and a Guide for Clinicians. Open Forum Infect Dis 2015; 2(3): ofv098.
  5. National Institute for Health and Care Excellence (NICE). NICE guideline - Pneumonia in adults: diagnosis and management (CG191), 2014.
  6. Bruns AH et al. Usefulness of consecutive C-reactive protein measurements in follow-up of severe community-acquired pneumonia. Eur Respir J 2008; 32(3): 726-732.
  7. Little P et al. Effects of internet-based training on antibiotic prescribing rates for acute respiratory-tract infections: a multinational, cluster, randomised, factorial, controlled trial. Lancet 2013; 382(9899): 1175-1182.
  8. Tonkin-Crane SKG et al. Clinician-targeted interventions to influence antibiotic prescribing behaviour for acute respiratory infections in primary care: an overview of systematic reviews (Review). Cohcrane Database of Systematic Reviews 2017; 7(9): CD012252.
  9. Emery P. Evidence-based review of biologic markers as indicators of disease progression and remission in rheumatoid arthritis. Rheumatol Int 2007; 27(9): 793-806.
  10. Verhagen DW et al. Prognostic value of serial C-reactive protein measurements in left-sided native valve endocarditis. Arch Intern Med 2008; 168(3): 302-307.
  11. Chalmers JD, Singanayagam A, Hill AT. C-Reactive Protein Is an Independent Predictor of Severity in Community-acquired Pneumonia. Am J Med 2008; 121(3):219-225.