1. Components: The Society for Vascular Surgery Lower Extremity Threatened Limb (SVS WIfI) classification system has three components:
   Wound
   Ischemia
   Foot Infection
2. Grades: Each component is graded on a spectrum from 0 (none) to 1 (mild) to 2 (moderate) to 3 (severe) according to the criteria outlined in Table II.
3. Classes: Based on grades assigned to each of the three individual components, a WIfI class is assigned.
   1. A patient with ischemic rest pain, an ABI of 0.30, no wound, and no signs of infection would be classified as Wound 0 Ischemia 3 foot Infection 0 or WIfI 030.
   2. A 55-year-old man with diabetes, dry gangrene of two toes, and a <2-cm rim of cellulitis at the base of the toes, but without systemic or metabolic toxicity has absent pedal pulses. The ABI is 1.5. The toe pressure is 35 mm Hg. He would be classified as Wound 2 Ischemia 2 foot Infection 1 or WIfI 221.
4. Stages: The four clinical stages were derived by Delphi Consensus (Table IV) and will require prospective validation. This process is intended to be iterative and is meant to reduce the number of clinical stages to a manageable and meaningful number; the stages should correlate with amputation risk (natural history of limb with that given clinical stage in the absence of revascularization). Using the same patient examples as above:
   1. A patient with ischemic rest pain, an ABI of 0.30, no wound, and no signs of infection would be classified as: Wound 0 Ischemia 3 foot Infection 0 or WIfI 030. The consensus clinical stage is 2 (low) with respect to risk of major limb amputation at one year.
   2. A 55-year-old man with diabetes, dry gangrene of two toes, and a <2-cm rim of cellulitis at the base of the toes, but without systemic or metabolic toxicity has absent pedal pulses. The ABI is 1.5. The toe pressure is 35 mm Hg. He would be classified as Wound 2 Ischemia 2 foot Infection 1 or WIfI 221. The clinical stage would be 4 (high risk of amputation).

ABI, Ankle-brachial index.