When bacteria (or viruses) infect a living organism, the body often responds with an inflammatory reaction, which is typically characterized by fever, an increase in white blood cell count, accelerated erythrocyte sedimentation rate (ESR) and elevated levels of various acute-phase reactants. When a patient presents with infectious inflammation due to an infection, it is clinically important to accurately distinguish between bacterial and viral infections early on, assess the severity of the infection and guide the appropriate use of antibiotics to prevent misuse. As reliable indicators of inflammation, inflammatory markers are commonly used to diagnose and monitor inflammatory conditions, as well as to guide antibiotic therapy. Widely used inflammatory markers include procalcitonin (PCT), interleukin-6 (IL-6), C-reactive protein (CRP) and serum amyloid A (SAA).
C-Reactive Protein (CRP)
CRP is an acute-phase protein synthesized by the liver in response to pro-inflammatory cytokines, particularly interleukin-6 (IL-6). It is one of the most widely used biomarkers for detecting inflammation due to its rapid increase in serum levels following an inflammatory stimulus.
Diagnosis of Infections and Inflammatory Diseases: Elevated CRP levels indicate bacterial infections, autoimmune diseases, and chronic conditions like rheumatoid arthritis and inflammatory bowel disease.
Risk Assessment in Cardiovascular Diseases: High-sensitivity CRP (hs-CRP) tests help assess cardiovascular risk, with elevated levels linked to a higher risk of myocardial infarction and stroke.
Monitoring Treatment Response: CRP levels track the effectiveness of anti-inflammatory and antimicrobial therapies, offering a quantitative measure of disease activity and treatment response.
Serum Amyloid A (SAA)
SAA is another acute-phase protein primarily produced by the liver. Its levels rise significantly in response to inflammation, and it serves as a precursor to amyloid A protein, which can deposit in tissues in chronic inflammatory states.
Early Detection of Inflammatory States: SAA levels increase more rapidly than CRP in response to inflammatory stimuli, making it a sensitive marker for early detection of inflammation.
Prognostic Value in Chronic Diseases: Persistent elevation of SAA is associated with chronic inflammatory diseases and can indicate a risk of complications such as amyloidosis.
Utility in Cancer and Autoimmune Disorders: SAA levels are elevated in certain cancers and autoimmune conditions, providing additional information for diagnosis and monitoring.
Incorporating both CRP and SAA assessments enhance diagnostic accuracy and provide a more comprehensive picture of the inflammatory state. For instance, in acute infections, CRP level confirms the presence of inflammation, while SAA level provides early detection and potentially guide the intensity of therapeutic interventions.
