From the Guidelines
C-reactive protein (CRP) is a crucial diagnostic marker for prosthetic joint infection (PJI) and should be measured in all patients with suspected PJI, with a cutoff value of 13.5 mg/L indicating potential infection. The measurement of CRP is a valuable tool in the diagnosis of PJI, with a sensitivity of 73% to 91% and a specificity of 81% to 86% 1. It is essential to interpret CRP results in the clinical context, as elevated levels can also be caused by other conditions such as rheumatoid arthritis, trauma, or recent surgery.
Diagnostic Approach
The diagnostic approach for PJI should include a combination of tests, such as:
- Serum CRP and erythrocyte sedimentation rate (ESR) measurements
- Joint aspiration with synovial fluid analysis
- Microbiological cultures
- Histopathological examination of periprosthetic tissue when available The American Academy of Orthopaedic Surgeons (AAOS) guidelines strongly recommend the use of ESR, CRP, and serum interleukin-6 testing for patients being assessed for peri-prosthetic joint infection 1.
Interpretation of Results
CRP levels typically peak 2-3 days after infection onset and normalize within 2-3 weeks after successful treatment, making it useful for monitoring treatment response 1. However, it is crucial to note that CRP is a non-specific inflammatory marker and can be elevated due to other conditions. The combination of abnormal results for at least 2 of 3 tests (CRP, ESR, and fibrinogen) can lead to accurate results for the diagnosis of infection, with a sensitivity of 93% and specificity of 100% 1.
Clinical Considerations
In clinical practice, it is essential to consider the patient's medical history, physical examination, and laboratory results when interpreting CRP levels. The use of antimicrobial therapy can reduce CRP levels, leading to false negatives, and therefore, blood samples should be collected before starting antibiotics 1. Additionally, the presence of underlying inflammatory arthropathy can make serologic tests harder to interpret 1.
Recent Developments
Recent studies have shown that the use of alpha-defensin laboratory tests can be highly accurate in the diagnosis of prosthetic joint infection, with a sensitivity of 97% and specificity of 96% 1. The combination of synovial fluid alpha-defensin and CRP tests can demonstrate a sensitivity of 97% and specificity of 100% for the diagnosis of periprosthetic joint infection 1.
From the Research
Measurement of CRP in Prosthetic Joint Infection
- The use of C-reactive protein (CRP) as a diagnostic tool for prosthetic joint infection (PJI) has been studied extensively, with varying results 2, 3, 4, 5, 6.
- A study published in 2020 found that serial CRP monitoring was not a reliable indicator of the successful eradication of PJI, with no statistical significance in mean CRP values between successful and unsuccessful treatment groups 2.
- Another study from 2017 found that CRP may misdiagnose PJI, particularly chronic and low-grade infections, with 32% of patients with positive cultures having normal CRP levels 3.
- In contrast, a 2022 study found that the CRP/albumin-to-globulin ratio (AGR) was a valuable test for diagnosing PJI, with an area under the curve (AUC) value of 0.902 4.
- A 2016 study evaluated the performance of leucocyte esterase, glucose, and CRP in the diagnosis of PJI, finding that leucocyte esterase had the highest sensitivity and specificity, while CRP had a sensitivity of 81.5% and specificity of 94.1% 5.
- A 2018 study found that the serum level of CRP alone cannot be used for the diagnosis of PJI, especially in those caused by organisms of low virulence, with 35.8% of patients with positive cultures having normal CRP levels 6.
Limitations of CRP in Diagnosing PJI
- The studies suggest that CRP has limitations as a diagnostic tool for PJI, particularly in cases of chronic or low-grade infections 3, 6.
- The use of CRP alone may lead to high false-negative rates, especially if the causative organism has low virulence 6.
- Other biomarkers, such as leucocyte esterase and the CRP/AGR ratio, may be more useful in diagnosing PJI 4, 5.