From the Guidelines
C-reactive protein (CRP) has a specificity of around 80% for diagnosing osteomyelitis, but its use as a sole diagnostic tool is limited due to its low specificity and sensitivity, not exceeding 0.85, as stated in the iwgdf/idsa guidelines on the diagnosis and treatment of diabetes-related foot infections 1. The specificity of CRP for diagnosing osteomyelitis is not highly reliable, as it is a general indicator of inflammation and infection, not specific to bone infections.
- CRP levels tend to rise more quickly with infection and fall more quickly with the resolution of infection, compared to ESR, as noted in the iwgdf/idsa guidelines 1.
- Serum values of CRP have consistently been found to be significantly higher in infected than noninfected DFUs and in patients with noninfected DFU than in those with no foot ulcer, with levels increasing significantly with the severity of infection 1.
- However, the use of CRP as a sole diagnostic tool is limited, and it should be used when uncertainty persists after clinical assessment, as recommended in the iwgdf/idsa guidelines 1.
- For diagnosing osteomyelitis, CRP is more useful when combined with other clinical findings, imaging studies, and additional laboratory tests, such as erythrocyte sedimentation rate (ESR) and white blood cell count.
- CRP is particularly valuable for monitoring treatment response in osteomyelitis, as a decreasing CRP level during antibiotic therapy suggests improvement, while persistently elevated levels may indicate treatment failure or complications, as seen in various studies 1.
- In practice, clinicians should not rely solely on CRP for diagnosing osteomyelitis but should use it as part of a comprehensive diagnostic approach, considering the limitations of CRP as a diagnostic tool, as stated in the iwgdf/idsa guidelines 1.
From the Research
Diagnostic Accuracy of C-Reactive Protein (CRP) for Osteomyelitis
- The specificity of CRP for diagnosing osteomyelitis varies across studies, with reported values ranging from 56% to 80% 2, 3.
- A study published in 2019 found that a CRP threshold of 7.9 mg/dL had a specificity of 80% for osteomyelitis, while a study from 2008 reported a specificity of 99.1% for the penumbra sign, which is associated with elevated CRP levels, in distinguishing osteomyelitis from bone tumors 2, 3.
- Another study from 2017 found that elevated levels of CRP had a specificity of 38.9% for the detection of long bone posttraumatic osteomyelitis relative to open bone biopsy and culture 4.
- The sensitivity and specificity of CRP for osteomyelitis diagnosis can be influenced by various factors, including the presence of comorbidities, the type of osteomyelitis, and the reference standard used for diagnosis 5, 2, 6.
Comparison with Other Diagnostic Markers
- CRP has been compared to other diagnostic markers, such as erythrocyte sedimentation rate (ESR) and procalcitonin (PCT), in the diagnosis of osteomyelitis 2, 6.
- A study from 2019 found that ESR had a sensitivity of 74% and specificity of 56% for osteomyelitis, while CRP had a sensitivity of 49% and specificity of 80% 2.
- Another study from 2020 proposed a systematic review to compare the diagnostic test accuracy of PCT and CRP in diagnosing osteomyelitis and septic arthritis in children and adolescents 6.