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What are the Optimal Cutoff Values for ESR and CRP to Diagnose Osteomyelitis in Patients with Diabetes-related Foot Infections?

Lavery, Lawrence A. DPM, MPH; Ahn, Junho BS; Ryan, Easton C. BS; Bhavan, Kavita MD; Oz, Orhan K. MD, PhD; La Fontaine, Javier DPM, MS; Wukich, Dane K. MD

Clinical Orthopaedics and Related Research®: July 2019 - Volume 477 - Issue 7 - p 1594–1602
doi: 10.1097/CORR.0000000000000718
2018 MUSCULOSKELETAL INFECTION SOCIETY PROCEEDINGS
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Background Distinguishing osteomyelitis from soft-tissue infection of the foot is important because osteomyelitis is associated with more operations, amputation, and prolonged antibiotic exposure. Both erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are routinely ordered inflammatory biomarkers for evaluating foot infection. When initial evaluation is inconclusive, advanced imaging is indicated, and high clinical or radiographic suspicion of osteomyelitis may indicate bone biopsy to identify organisms and antibiotic sensitivity. Although ESR and CRP levels are helpful for distinguishing osteomyelitis from soft-tissue infections in patients with diabetes-related foot infections, parameters regarding optimal cutoff values for those tests have not, to our knowledge, been defined.

Questions/purposes (1) What are the optimal cutoff values for ESR and CRP to differentiate osteomyelitis from soft-tissue infection in patients with diabetes-related foot infection? (2) Can a diagnostic algorithm be derived to guide interpretation of ESR and CRP to improve recognition of osteomyelitis in the setting of diabetic foot infection?

Methods The medical records of 1842 patients between 18 and 89 years of age treated at our institution between January 1, 2010 and February 6, 2017 for foot infection were reviewed. For inclusion, patients must have had a diagnosis of diabetes mellitus, moderate or severe infection, ESR and CRP values within 72 hours of admission, either advanced imaging (MRI or single-positron emission computed tomography/computed tomography [SPECT/CT]) or bone biopsy during admission and must not have had comorbidities that could affect ESR and CRP, such as autoimmune disorders. As such, 1489 patients were excluded, and 353 patients were included in the study. Osteomyelitis was diagnosed by positive bone culture or histopathology. Osteomyelitis was considered to be absent if there was a negative MRI or SPECT/CT result, or negative bone culture and histology findings if imaging was inconclusive. We identified 176 patients with osteomyelitis and 177 with soft-tissue infection. A blinded investigator performed the statistics. Optimal cutoffs of ESR and CRP were determined using receiver operative characteristic (ROC) analysis. A diagnostic algorithm was determined using epidemiologic principles of screening evaluations.

Results An ESR of 60 mm/h and a CRP level of 7.9 mg/dL were determined to be the optimal cutoff points for predicting osteomyelitis based on results of the ROC analysis. The ESR threshold of 60 mm/h demonstrated a sensitivity of 74% (95% confidence interval [CI], 67–80) and specificity of 56% (95% CI, 48–63) for osteomyelitis, whereas the CRP threshold of 7.9 mg/dL had a sensitivity of 49% (95% CI, 41–57) and specificity of 80% (95% CI, 74–86). If the ESR is < 30 mm/h, the likelihood of osteomyelitis is low. However, 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.

Conclusions While ESR is better for ruling out osteomyelitis initially, CRP helps distinguish osteomyelitis from soft-tissue infection in patients with high ESR values. Further prospective studies addressing the prognostic value of ESR and CRP are needed, and a more comprehensive diagnostic algorithm should be developed to include other diagnostic tests such as probe-to-bone and imaging.

Level of Evidence Level III, diagnostic study.

L. A. Lavery, E. C. Ryan, J. L. Fontaine, Department of Plastic Surgery, University of Texas Southwestern Medical Center, Dallas, Texas, USA

J. Ahn, D. K. Wukich, Department of Orthopaedic Surgery, University of Texas Southwestern Medical Center, Dallas, Texas, USA

K. Bhavan, Department of Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA

O. K. Oz, Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA

E. C. Ryan, Department of Plastic Surgery, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, Texas 75390, USA, Email: easton.ryan@utsouthwestern.edu

Each author certifies that he or she has no commercial associations (e.g. consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article.

All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request.

Clinical Orthopaedics and Related Research® neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDA approval status, of any drug or device before clinical use.

Each author certifies that his or her institution approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.

Received August 09, 2018

Accepted February 21, 2019

© 2019 Lippincott Williams & Wilkins LWW
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