C-reactive protein (CRP) and procalcitonin (PCT) are biomarkers commonly used in clinical settings to assess inflammation, infection, and sepsis. These markers help guide diagnosis, treatment decisions, and prognostication in various medical conditions.
C-Reactive Protein (CRP)
CRP is an acute-phase protein produced by the liver in response to inflammation. Its levels rise rapidly in response to infection, tissue injury, and other inflammatory conditions. It’s a non-specific marker, meaning it can be elevated due to various conditions, not just infections
Normal Levels:
- Normal Range: <5 mg/L
Clinical Significance:
- Infection: Elevated CRP levels indicate acute inflammation and can be used to monitor the response to treatment in infections.
- Inflammation: CRP is non-specific and can be elevated in various inflammatory conditions, including autoimmune diseases, cardiovascular diseases, and malignancies.
- Sepsis: High CRP levels are commonly seen in sepsis, although CRP alone cannot distinguish between bacterial and non-bacterial causes of inflammation.
Advantages:
- Rapid Response: CRP levels increase within 6-12 hours of the onset of inflammation and peak at around 48 hours.
- Monitoring: Useful for monitoring the effectiveness of treatment and disease progression.
Limitations:
- Non-Specificity: Elevated CRP levels do not pinpoint the specific cause of inflammation and can be influenced by various factors, including trauma, surgery, and chronic diseases.
Procalcitonin (PCT)
Procalcitonin is a precursor of the hormone calcitonin, produced by the thyroid gland. In response to bacterial infection, PCT is released into the bloodstream by various tissues throughout the body. During bacterial infections, certain cells (particularly those involved in the immune response) start producing large amounts of PCT.
Normal Levels:
- Normal Range: <0.05 ng/mL
- Clinical Cutoffs:
- <0.1 ng/mL: Low likelihood of bacterial infection
- 0.1-0.5 ng/mL: Possible bacterial infection; clinical correlation needed
- >0.5 ng/mL: Likely bacterial infection
- >2 ng/mL: Strongly suggestive of sepsis or severe bacterial infection
Clinical Significance:
- Bacterial Infection: PCT levels rise significantly in bacterial infections and are used to differentiate bacterial from viral infections.
- Sepsis: High PCT levels are strongly associated with bacterial sepsis and can aid in early diagnosis and management.
- Antibiotic Stewardship: PCT can help guide antibiotic therapy decisions, potentially reducing unnecessary antibiotic use.
Advantages:
- Specificity for Bacterial Infections: More specific for bacterial infections compared to CRP, especially useful in differentiating bacterial from viral infections.
- Kinetics: PCT levels rise within 3-6 hours of bacterial infection onset, peak at 12-24 hours, and decrease as the infection resolves.
Limitations:
- Cost: PCT testing can be more expensive compared to CRP.
- Influencing Factors: PCT levels can be influenced by non-infectious conditions such as major surgery, trauma, and certain cancers.
Clinical Applications
- Differentiating Infections:
- CRP: Useful for detecting inflammation but less specific in distinguishing between bacterial and viral infections.
- PCT: Superior in identifying bacterial infections and guiding antibiotic therapy.
- Monitoring Treatment:
- Both CRP and PCT can be used to monitor the effectiveness of treatment in infections and sepsis. Decreasing levels indicate a positive response to therapy.
- Sepsis Management:
- CRP: Elevated in sepsis but non-specific.
- PCT: Elevated levels strongly suggest bacterial sepsis, aiding in early diagnosis and management.