medwireNews: A composite algorithm including the calprotectin biomarker can help physicians decide whether a diabetic foot ulcer needs antibiotic therapy, say researchers.
The algorithm, which includes the wound exudate calprotectin (a marker of neutrophilic inflammation), venous white cell count, C-reactive protein (CRP) levels, and ulcer area, helped distinguish non-infected from mildly infected diabetic foot ulcers, report the INDUCE study authors John Ingram (Cardiff University, UK) and colleagues.
The algorithm had a specificity of 0.81 but an area under the receiver operating characteristic curve of only 0.68, making it unsuitable for use in primary care in its current form, the researchers note. Nevertheless, the good specificity “provides some much-needed objective evidence to help clinicians avoid mass antibiotic prescribing in noninfected diabetic foot ulcers,” they write in Diabetic Medicine.
While moderate to severe diabetic foot ulcer infection is straightforward to diagnose from clinical parameters, the team points out that it is far more difficult to distinguish between a non-infected or mildly infected foot ulcer in the community setting, where point-of-care tests can be lacking.
They tested the diagnostic ability of four inflammatory biomarkers – venous white cell count, CRP, procalcitonin, and calprotectin – in 34 individuals with non-infected and 27 with mildly infected diabetic foot ulcers (defined by clinicians’ overall impressions from two assessments 1 week apart) in a community setting.
Procalcitonin levels were below the lower limit of assay detection in nearly 70% of cases, leading to this variable being excluded from the algorithm.
Median wound exudate calprotectin levels, however, were nearly twice as high in samples from patients with mildly infected versus non-infected diabetic foot ulcers, at 1437 and 879 ng/mL, respectively.
Differences were also seen for the other biomarkers, with significantly higher venous white cell counts and CRP levels in patients with mildly infected versus non-infected foot ulcers of 8.15 versus 7.43 109cells/L and 9.0 versus 6.0 mg/L, respectively.
The researchers substituted venous procalcitonin for ulcer area, which was a median 1.32 cm2 in those with mild infection versus 0.22 cm2 in those with no infection. This generated a composite algorithm with a sensitivity of 0.64, a positive predictive value of 0.73, and a negative predictive value of 0.75 for mild infection.
Importantly, the researchers note: “The parameters included in our algorithm are, or soon will be, available at point of care, which is an important consideration when most diabetic foot ulcer care occurs in the community and antibiotic decisions have to be made swiftly.”
By Catherine Booth
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