Study defends use of SIRI as a practical marker in assessing diabetic foot infection severity

A recent response to critiques highlights ongoing efforts to validate the systemic inflammatory response index (SIRI) as an accessible tool for assessing severe diabetic foot infections, amid calls for more robust prospective evidence and refinement.

A response published by Dovepress has defended a study examining whether the Systemic Inflammatory Response Index, or SIRI, could help identify severe diabetic foot infection, while also acknowledging calls for stronger prospective evidence. The authors said the work was intended as an association study rather than proof of causation, and they pointed to plans for a larger prospective project to test the idea further. Diabetic foot infection is clinically important because, as NICE and the IDSA-IWGDF guidance make clear, severity determines treatment intensity, the need for hospital care and the risk of limb loss.

In their reply, the authors argued that their severity definition followed international guidance rather than relying on a single blood-cell abnormality. Current NICE and IDSA-IWGDF recommendations classify foot infections by local and systemic signs, ranging from uninfected to severe disease, and include markers such as fever, tachycardia and abnormal white-blood-cell counts in more serious cases. The authors said that because SIRI combines neutrophils, monocytes and lymphocytes, it can capture a broader inflammatory picture than neutrophils alone, which they said supported its use as a practical screening indicator.

They also addressed concerns about the statistical model behind the paper. After performing bootstrap validation, the team said the calibration curve supported the model’s performance, while variance inflation factor testing suggested no major multicollinearity, with all values below 5. That matters because diabetes-related foot infection research often depends on careful grading and robust models to guide decisions on admission, imaging, antibiotics and surgery, according to the IDSA-IWGDF guidance and earlier consensus literature on diabetic foot infection severity.

The authors said they still see value in the criticism raised by readers, including the suggestion that future analyses remove white-cell components from the severity definition to test the independence of SIRI more cleanly. They said that sensitivity analysis would be a useful addition to subsequent work, but that the current paper’s main purpose was to explore association rather than establish a causal link. They added that their ongoing study has not yet been made public, though the current dataset can be obtained from the corresponding author on reasonable request.

More broadly, the exchange reflects a wider challenge in diabetic foot care: clinicians need biomarkers that are simple, available and informative, yet still aligned with accepted definitions of infection severity. SIRI is a general inflammation index, built from the ratio of neutrophils and monocytes to lymphocytes, and has been discussed in other inflammatory settings as a marker of immune activation. But the guidance cited by the authors and independent clinical summaries still place greatest weight on a combination of local findings, systemic signs and standard laboratory tests when deciding how severe a diabetic foot infection really is.