Test Catalog

Test ID: CRP    
C-Reactive Protein (CRP), Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Detecting systemic inflammatory processes


Detecting infection and assessing response to antibiotic treatment of bacterial infections


Differentiating between active and inactive disease forms with concurrent infection

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

C-reactive protein (CRP) is one of the most sensitive acute-phase reactants for inflammation. CRP is synthesized by the liver and consists of 5 identical polypeptide chains that form a 5-membered ring with a molecular weight of 105,000 daltons. Complexed CRP activates the classical complement pathway. The CRP response frequently precedes clinical symptoms, including fever.


CRP elevations are nonspecific and may be useful for the detection of systemic inflammatory processes; to assess treatment of bacterial infections with antibiotics; to detect intrauterine infections with concomitant premature amniorrhexis; to differentiate between active and inactive forms of disease with concurrent infection, eg, in patients suffering from systemic lupus erythematosus or colitis ulcerosa; to therapeutically monitor rheumatic disease and assess anti-inflammatory therapy; to determine the presence of postoperative complications at an early stage, such as infected wounds, thrombosis, and pneumonia; and to distinguish between infection and bone marrow rejection. Postoperative monitoring of CRP levels of patients can aid in the recognition of unexpected complications (persisting high or increasing levels).


Measuring changes in the concentration of CRP provides useful diagnostic information about the level of acuity and severity of a disease. It also allows judgments about the disease genesis. Persistence of a high serum CRP concentration is usually a grave prognostic sign that generally indicates the presence of an uncontrolled infection.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

< or =8.0 mg/L

Interpretation Provides information to assist in interpretation of the test results

In normal healthy individuals, C-reactive protein (CRP) is a trace protein (<8 mg/L).


Elevated values are consistent with an acute inflammatory process.


After onset of an acute phase response, the serum CRP concentration rises rapidly (within 6-12 hours and peaks at 24-48 hours) and extensively. Concentrations above 100 mg/L are associated with severe stimuli such as major trauma and severe infection (sepsis).

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

C-reactive protein (CRP) response may be less pronounced in patients suffering from liver disease.


Elevated CRP values are nonspecific and should not be interpreted without a complete clinical history.

Clinical Reference Recommendations for in-depth reading of a clinical nature

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Sixth edition. Edited by N Rafai, AR Horvath, CT Wittwer. Elsevier, 2018