From the Guidelines
An elevated CRP workup should begin with a thorough history and physical examination, followed by serum ESR and CRP testing, as recommended by the American Academy of Orthopaedic Surgeons (AAOS) guidelines 1.
Initial Evaluation
The initial evaluation of an elevated CRP should include:
- A complete blood count to screen for infections or other inflammatory conditions
- A comprehensive metabolic panel to assess organ function
- Urinalysis to screen for urinary tract infections
- Targeted tests based on clinical suspicion, such as chest X-ray for respiratory symptoms or blood cultures for suspected infection
Additional Testing
Additional testing may include:
- Autoimmune markers (ANA, RF, ESR) to evaluate for autoimmune disorders
- Imaging studies, such as radiographs or advanced imaging modalities, to assess for structural abnormalities or inflammation
- Specialty referrals, such as rheumatology or infectious disease, for further evaluation and management
Interpretation of CRP Results
The degree of CRP elevation can provide clues to the underlying cause, with:
- Very high levels (>100 mg/L) typically suggesting bacterial infection
- Moderate elevations may occur in viral infections or inflammatory conditions
- Serial CRP measurements can be useful to monitor treatment response
Recent Guidelines
Recent guidelines, such as the 2023 update of the ACR Appropriateness Criteria for imaging after total knee arthroplasty, recommend the use of CRP and joint aspiration as the most useful tools to diagnose infection 1.
Alpha-Defensin Testing
Alpha-defensin testing has also been shown to be highly accurate in the diagnosis of prosthetic joint infection, with a sensitivity of 97% and specificity of 96% when used alone, and a sensitivity of 97% and specificity of 100% when combined with CRP testing 1.
From the Research
Elevated CRP Workup
Elevated C-reactive protein (CRP) levels are a sensitive biomarker of inflammation, and have been implicated in various diseases, including cardiovascular disease and certain cancers 2. The workup for elevated CRP involves identifying the underlying cause of inflammation.
Possible Causes of Elevated CRP
- Infection: CRP levels can rise in response to bacterial infection, tissue injury, and autoimmunity 2, 3
- Inflammatory diseases: Conditions such as rheumatoid arthritis can cause elevated CRP levels 4
- Cardiovascular disease: Elevated CRP levels have been linked to an increased risk of cardiovascular disease 2
- Cancer: Certain types of cancer can cause elevated CRP levels 2
Diagnostic Approach
- Medical history and physical examination to identify potential causes of inflammation
- Laboratory tests, such as complete blood count and blood chemistry tests, to rule out underlying infections or inflammatory diseases
- Imaging studies, such as X-rays or CT scans, to evaluate for tissue injury or infection
- Measurement of other inflammatory biomarkers, such as procalcitonin (PCT), to help differentiate between causes of inflammation 5
Treatment
- Treatment of the underlying cause of inflammation, such as antibiotics for bacterial infections or anti-inflammatory medications for rheumatoid arthritis
- Glucocorticoids, such as prednisone, may be used to reduce inflammation in certain conditions, such as community-acquired pneumonia 5
- Nonsteroidal anti-inflammatory drugs (NSAIDs) may be used to reduce inflammation, but their effect on CRP levels can vary depending on the specific NSAID used 4