From the Guidelines
To rule out osteomyelitis, order an MRI as the primary imaging modality, as it has the highest sensitivity and specificity for diagnosing osteomyelitis, and consider plain radiographs as an initial step, although they have relatively low sensitivity and specificity. When interpreting the results, consider the clinical context and the likelihood of osteomyelitis, as recommended by the Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections 1.
Imaging Studies
- Start with plain radiographs (X-rays) of the affected area, which can provide some information regarding bony abnormalities, although they have only moderately helpful performance characteristics, with a pooled sensitivity of 0.54 and specificity of 0.68 for osteomyelitis 1.
- Follow with an MRI, which is the most sensitive imaging modality with high sensitivity and specificity for osteomyelitis, and is recommended as the study of choice for patients who require initiate treatment for presumptive osteomyelitis 1.
- Consider bone scans (three-phase technetium-99m) or CT scans as alternative imaging modalities when MRI is contraindicated or not available, although they have lower sensitivity and specificity compared to MRI.
Laboratory Tests
- Blood tests, including complete blood count (CBC), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP), can be useful in supporting the diagnosis of osteomyelitis, as they are typically elevated in infection.
- Blood cultures should be obtained before starting antibiotics, as they may identify the causative organism in some cases of osteomyelitis.
Definitive Diagnosis
- If the diagnosis remains uncertain, bone biopsy with culture remains the gold standard, providing definitive diagnosis and guiding antibiotic therapy, as recommended by the Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections 1.
From the Research
Laboratory Tests to Rule Out Osteomyelitis
To diagnose or rule out osteomyelitis, several laboratory tests can be ordered, including:
- Erythrocyte sedimentation rate (ESR) 2, 3, 4, 5, 6
- C-reactive protein (CRP) 2, 3, 4, 5, 6
- Procalcitonin (PCT) 5
- White blood cell count (WBC) 2
- Blood cultures and/or histopathology to confirm the diagnosis of osteomyelitis 2, 3
Interpretation of Laboratory Results
The interpretation of laboratory results is crucial in diagnosing osteomyelitis. For example:
- Elevated ESR and CRP levels can indicate the presence of an inflammatory condition, such as osteomyelitis 2, 3, 4, 5, 6
- A high PCT level can be useful in discriminating patients with bone infection 5
- The combination of ESR and CRP can be used to monitor treatment outcomes in diabetic foot osteomyelitis 2
- The cutoff points of ESR and CRP can be used to predict osteomyelitis recurrence 4
Clinical Considerations
When ordering laboratory tests to rule out osteomyelitis, clinicians should consider the following:
- The patient's medical history, including the presence of diabetes or other underlying conditions 2, 5
- The location and duration of the wound or infection 2, 3
- The presence of other inflammatory conditions that may affect laboratory results 6
- The need for imaging studies, such as magnetic resonance imaging (MRI), to confirm the diagnosis of osteomyelitis 3, 5