Can Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) differentiate between cellulitis and acute hematogenous osteomyelitis in diabetic patients?

From the Guidelines

ESR and CRP cannot reliably differentiate between cellulitis and acute hematogenous osteomyelitis in diabetic patients. Both inflammatory markers are typically elevated in both conditions, making them useful for detecting inflammation but not for distinguishing between these specific infections. While higher values may suggest osteomyelitis, there is significant overlap in the ranges seen in both conditions. Diabetic patients often have baseline elevations in these markers, further complicating interpretation.

Key Points to Consider

• The diagnosis of osteomyelitis in diabetic patients is challenging and requires a comprehensive approach, including physical examination, imaging studies, and laboratory tests 1.
• The probe-to-bone test, plain X-rays, and ESR or CRP can be used as initial studies to diagnose osteomyelitis, but MRI is the most sensitive imaging method for diagnosing osteomyelitis 1.
• Blood cultures should be obtained before starting antibiotics to identify the causative organism in hematogenous osteomyelitis.
• A definitive diagnosis of osteomyelitis usually requires positive results on both histological and microbiological examinations of an aseptically obtained bone sample 1.
• The IWGDF/IDSA guidelines recommend using a combination of diagnostic tests, including probe-to-bone, serum inflammatory markers, plain X-ray, and MRI or radionuclide scanning, to diagnose osteomyelitis 1.

Diagnostic Approach

For accurate diagnosis, clinicians should combine ESR and CRP tests with other diagnostic modalities, such as MRI, bone scans, or bone biopsy. Physical examination findings like bone tenderness, depth of infection, and presence of ulcers provide important clinical context. The diagnostic approach should be comprehensive rather than relying solely on inflammatory markers, especially in diabetic patients where the stakes of missed bone infection are high 1.

From the Research

Differentiation between Cellulitis and Acute Hematogenous Osteomyelitis

• Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) are commonly used inflammatory biomarkers to evaluate foot infections in diabetic patients.
• A study published in 2019 2 determined the optimal cutoff values for ESR and CRP to diagnose osteomyelitis in patients with diabetes-related foot infections.
• The optimal cutoff values were found to be an ESR of 60 mm/h and a CRP level of 7.9 mg/dL, with sensitivity and specificity of 74% and 56% for ESR, and 49% and 80% for CRP, respectively.

Diagnostic Algorithm

• The study 2 suggested a diagnostic algorithm using ESR and CRP to improve recognition of osteomyelitis in diabetic foot infections.
• If the ESR is < 30 mm/h, the likelihood of osteomyelitis is low.
• If ESR is > 60 mm/h and CRP level is > 7.9 mg/dL, the likelihood of osteomyelitis is high, and treatment of suspected osteomyelitis should be strongly considered.
• While ESR is better for ruling out osteomyelitis initially, CRP helps distinguish osteomyelitis from soft-tissue infection in patients with high ESR values.

Limitations and Challenges

• Diagnosing infection in the diabetic foot can be challenging, and determining whether infection is present in bone can be especially difficult 3.
• Soft-tissue cultures may not predict bone cultures with sufficient reliability, and bone and deep soft tissue specimens should be obtained from patients with suspected osteomyelitis 4.
• Imaging tests, such as magnetic resonance imaging, and newer molecular microbial techniques may be helpful in diagnosing diabetic foot infections 3, 5, 6.