From the Guidelines
Acute phase reactants are proteins whose blood concentrations change rapidly in response to inflammation or tissue injury, and the most clinically significant ones include C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), ferritin, fibrinogen, and procalcitonin, as noted in a study published in 2017 1.
Definition and Examples of Acute Phase Reactants
These proteins are primarily produced by the liver in response to inflammatory cytokines, especially interleukin-6 (IL-6), IL-1, and tumor necrosis factor-alpha (TNF-α). During an inflammatory response, CRP levels can increase up to 1,000-fold within 24-48 hours, making it particularly useful for detecting acute inflammation. Some key points about acute phase reactants include:
- ESR measures the rate at which red blood cells settle in a tube and increases during inflammation due to higher levels of fibrinogen and other acute phase proteins.
- These markers are valuable diagnostic tools for monitoring inflammatory conditions like infections, autoimmune diseases, and tissue damage.
- However, they are non-specific indicators of inflammation and must be interpreted alongside clinical findings and other laboratory tests to determine the underlying cause of inflammation, as highlighted in a study from 2011 1.
Clinical Use of Acute Phase Reactants
In clinical practice, acute phase reactants are used to:
- Monitor the response to therapy in patients with inflammatory conditions.
- Distinguish between bacterial and viral infections, although their usefulness in this regard is limited, as noted in a study from 2005 1.
- Assess the severity of inflammation and guide treatment decisions. For example, a study published in 2017 1 found that CRP and ESR are nearly universally elevated in patients with Kawasaki disease, and that the degree of elevation can be helpful in diagnosing and managing the condition.
Limitations and Potential Biases
It is essential to consider the limitations and potential biases of acute phase reactants, including:
- They are non-specific indicators of inflammation and can be elevated in a variety of conditions.
- Their levels can be influenced by factors such as age, sex, and comorbidities.
- They may not be useful in distinguishing between bacterial and viral infections, as noted in a study from 2011 1. Overall, acute phase reactants are valuable diagnostic tools that can provide important information about the presence and severity of inflammation, but their interpretation requires careful consideration of the clinical context and other laboratory findings, as highlighted in a study from 2017 1.
From the Research
Definition of Acute Phase Reactant
- Acute phase reactants (APRs) are a heterogeneous group of plasma proteins whose concentration either increases or decreases by at least 25% during an inflammatory process 2.
- The acute phase response is a systemic response that usually follows a physiological condition that takes place in the beginning of an inflammatory process, aiming to restore homeostasis 3.
Characteristics of Acute Phase Reactants
- APRs can be either positive (upregulated) or negative (downregulated) during inflammatory reactions 3.
- Examples of positive acute phase reactants include C-reactive protein (CRP), serum amyloid A (SAA), fibrinogen, and ferritin 2, 3.
- Examples of negative acute phase reactants include albumin, transferrin, and antithrombin 3.
Clinical Significance of Acute Phase Reactants
- APRs are elevated in various conditions, including infection, trauma, burns, tissue infarction, inflammatory conditions, and advanced malignancy 2.
- APRs, such as CRP and SAA, can be used as diagnostic tools to predict the severity of infection and differentiate between viral and bacterial infections 2, 4.
- APRs are also involved in various diseases, including cardiovascular disease, systemic lupus erythematosus, rheumatoid arthritis, and psoriasis 2, 3.