Assessing diabetes-related foot ulcers for infection

For a diabetes-related foot ulcer to be considered infected, at least 2 of the following features should be presentCommons, 2021Senneville, 2023:

  • local swelling or induration
  • erythema extending more than 0.5 cm in any direction from the wound
  • local tenderness or pain
  • local increased warmth
  • purulent discharge.

Other causes of inflammation (eg trauma, gout, thrombosis) should be considered.

Note: Culture of a superficial swab may identify organisms that are colonising the wound rather than causing infection.

Culture of tissue samples obtained by biopsy or aspiration can guide antibiotic therapy. However, culture of a superficial swab of an ulcer base may identify organisms that are colonising the wound rather than causing infection, so interpret results with care. Do not collect specimens from noninfected ulcers because antibiotic therapy is not indicated.

Note: Do not collect specimens for culture from noninfected ulcers.

For information on the severity classification for infections of diabetes-related foot ulcers, see Severity classification for infections of diabetes-related foot ulcers.

Figure 1. Severity classification for infections of diabetes-related foot ulcers

Commons, 2021Senneville, 2023

Mild infection of diabetes-related foot ulcers

  • Involve only the skin and subcutaneous tissue.
  • Erythema extends up to 2 cm from the wound margin.
  • Systemic features of infection are not present.

Moderate infection of diabetes-related foot ulcers

  • Involve structures deeper than the skin or subcutaneous tissues (eg muscle, bone, joint, tendon).
  • Erythema extends more than 2 cm from the wound margin.
  • Infection is not associated with SIRS (see below).

Severe infection of diabetes-related foot ulcers is an infection associated with SIRS, defined by the presence of 2 or more of:

  • abnormal temperature (more than 38°C or less than 36°C)
  • heart rate more than 90 beats/minute
  • respiratory rate more than 20 breaths/minute
  • white cell count more than 12 × 109/L or less than 4 × 109/L, or more than 10% immature [band] forms.
Note: SIRS = systemic inflammatory response syndrome

Bone or joint infection (osteomyelitis or septic arthritis) complicate a significant proportion of diabetes-related foot ulcers, and are associated with a high risk of major amputation. Any bone or joint may be affected but the forefoot (toes and metatarsals) is most frequently involvedAicale, 2020. For patients with suspected osteomyelitis, recommended initial investigations includeCommons, 2021Senneville, 2023:

  • probe-to-bone test
  • blood sample to assess C-reactive protein (CRP) or procalcitonin
  • X-ray.