Combined Clinical and Laboratory Testing Improves Diagnostic Accuracy for Osteomyelitis in the Diabetic Foot

The purpose of this investigation was to examine the value of using routinely available clinical and laboratory tests in combination to distinguish osteomyelitis from cellulitis in a diabetic population with mild to moderately infected forefoot ulcers. We conducted a case-control study of 54 diabetic patients with 54 locally infected ulcers admitted to a university-affiliated tertiary-care hospital over a 4.5-year period. A total of 30 clinical and laboratory characteristics obtained at admission were tested for their association with pathology-proven osteomyelitis using logistic regression techniques. Ulcer depth greater than 3 mm (univariate odds ratio 10.4, P = .001) and C-reactive protein greater than 3.2 mg/dL (univariate odds ratio 10.8, P < .001) were the most informative individual clinical and laboratory tests for differentiating osteomyelitis from cellulitis. Adding C-reactive protein also significantly improved upon the accuracy of the study's best clinical testing strategy (area under the curve improved from 0.80 to 0.88, P = .040). Strategies that combined ulcer depth with serum inflammatory markers proved most useful in detecting ulcerated patients with concomitant bone infections (sensitivity 100% [95% CI 89.7%–100%] for both ulcer depth greater than 3 mm or C-reactive protein greater than 3.2 mg/dL, and ulcer depth greater than 3 mm or erythrocyte sedimentation rate greater than 60 mm/h). We conclude that considering clinical and laboratory findings together can significantly improve our diagnostic accuracy for osteomyelitis in the diabetic foot. The specific combination of ulcer depth with serum inflammatory markers appears to be a particularly sensitive strategy that may allow for greater detection of early diabetic osteomyelitis. Level of Clinical Evidence: 3

Key Words: C-reactive protein, case control study, diabetic foot infection, diagnosis, erythrocyte sedimentation rate, osteomyelitis, ulcer