From the Guidelines
To rule out osteomyelitis, I recommend obtaining a complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and blood cultures, as well as considering a probe-to-bone test, plain X-rays, and MRI, as suggested by the most recent guidelines 1. These tests should be ordered before starting antibiotics whenever possible. The CBC may show leukocytosis with left shift in acute infection.
Key Laboratory Tests
- ESR and CRP are inflammatory markers that are typically elevated in osteomyelitis, with ESR often exceeding 70 mm/hr and CRP rising above 50 mg/L in active bone infection.
- Blood cultures should be collected from two separate sites to identify the causative organism, which is crucial for targeted antibiotic therapy.
Additional Considerations
- Additional tests to consider include procalcitonin, which may help distinguish bacterial from non-bacterial causes, and bone-specific alkaline phosphatase, which can be elevated during bone remodeling.
- Imaging studies such as X-rays, MRI, or bone scans should also be considered, as no single laboratory test can definitively rule out osteomyelitis.
- The diagnosis ultimately requires correlation of laboratory, clinical, and imaging findings, as recommended by recent studies 1.
Imaging Studies
- MRI is the most useful imaging modality for diagnosing osteomyelitis, especially when the diagnosis is in doubt or when advanced imaging is needed 1.
- Plain X-rays can provide anatomic evaluation and demonstrate findings of chronic osteomyelitis, but may not be sensitive enough for early diagnosis 1.
From the Research
Laboratory Investigations for Osteomyelitis
To rule out osteomyelitis, several laboratory investigations can be useful, including:
- Erythrocyte sedimentation rate (ESR) 2, 3, 4, 5, 6
- C-reactive protein (CRP) 2, 3, 4, 5, 6
- Procalcitonin (PCT) 4, 6
- White blood cell count (WBC) 4, 5
Interpretation of Laboratory Results
The interpretation of these laboratory results is crucial in diagnosing osteomyelitis. For example:
- A normal ESR and CRP <5 mg/L may reassure the clinician that no further urgent investigation is required in patients with a clinically low level of suspicion of osteomyelitis 2
- An ESR >30 mm/h and/or CRP >10-30 mg/L may indicate the need for further definitive investigation in patients with any suspicion of osteomyelitis 2
- The cutoff points of CRP ≥5 mg/l and ESR ≥20 mm/h can be used to predict osteomyelitis recurrence 3
- PCT levels can be used to discriminate patients with bone infection, with a best cut-off value of 0.085 ng/ml 6
Clinical Application
These laboratory investigations can be used in clinical practice to: