Diabetic foot ulcer and deep-seated foot infection

A punched-out ulcer on a pressure point with a rim of callus, often painless; surrounding erythema, warmth and swelling where infected; dusky or black tissue where ischaemic.

The erythema that signals infection and the pallor or duskiness that signals ischaemia are both colour-based and both fail here, which is one reason outcomes are worse. Use the tone-independent examination instead: compare temperature with the other foot using the back of your hand, feel for fluctuance and crepitus, probe the ulcer for depth and for bone, look for swelling and for loss of the normal skin creases, and smell the wound. Do not expect frank blackening: necrotic tissue in brown and black skin may read as a darkening of established pigment rather than an obvious black eschar, so gangrene can look less dramatic than it is. That is clinical reasoning rather than a cited finding - no source is given for it here because none could be traced - so judge viability on texture, temperature, demarcation and smell rather than on colour. Check pulses and capillary refill rather than judging perfusion from colour, and examine the contralateral foot as your baseline.

• An ulcer at a pressure point with a callus rim, in a foot that does not hurt, is the classic neuropathic ulcer - painlessness is the disease, not reassurance
• Probe the ulcer. Depth, a sinus, or bone felt at the base changes this from a wound to a deep infection
• Swelling, warmth and a change in shape of the foot, with the skin intact, is the presentation that gets missed
• Ask about how long it has been there, and whether the patient noticed it or someone else did
• Assess both the neuropathy and the circulation, because they determine what kind of problem this is

• Cellulitis — A hot swollen foot in a person with diabetes is treated as a diabetic foot problem, not as simple cellulitis - and acute Charcot arthropathy mimics infection exactly, often with intact skin
• Necrotising fasciitis and necrotising soft tissue infection — Pain out of proportion, crepitus or rapid progression in a diabetic foot is a surgical emergency and outranks every pathway on this page
• Venous eczema, lipodermatosclerosis and venous leg ulcers — Venous ulcers sit in the gaiter area above the malleolus and are usually painful with surrounding pigmentation; neuropathic ulcers sit on pressure points and are usually painless
• Erysipelas — Both present with a red hot foot, but erysipelas has a sharply demarcated raised edge and the diabetic foot needs the foot pathway regardless

1. Take the shoes and socks off and look at both feet, every time. A person with diabetes and neuropathy will not report an ulcer they cannot feel
2. Under 18s are in scope and NG19 addresses them. The limb-threatening and life-threatening criteria in 1.4.1 carry no age qualifier. For a young person aged 12 to 17, NG19 routes a suspected diabetic foot problem through the paediatric or transitional diabetes team to an appropriate specialist, and recommendation 1.6.9 says to seek specialist advice before prescribing antibiotics for a suspected diabetic foot infection in anyone under 18. Only NG19's antibiotic tables are restricted to adults
3. Apply NG19's referral rule, which is about urgency rather than diagnosis. A limb-threatening or life-threatening problem - ulceration with fever or sepsis, ulceration with limb ischaemia, concern about deep soft tissue or bone infection with or without ulceration, or gangrene - is referred immediately to acute services, with the multidisciplinary foot care service informed
4. For all other active diabetic foot problems, NG19 says refer within 1 working day to the multidisciplinary foot care or foot protection service, for triage within one further working day. An active problem is ulceration, infection, chronic limb-threatening ischaemia, gangrene, suspected acute Charcot arthropathy, or an unexplained hot swollen foot with a change in colour
5. Suspect acute Charcot arthropathy if there is redness, warmth, swelling or deformity - NG19 says particularly when the skin is intact, especially with peripheral neuropathy or renal failure, and to think of it even when there is no deformity and no reported pain. Refer within 1 working day and keep the foot non-weight-bearing until definitive treatment starts
6. Arrange a weight-bearing X-ray of the foot and ankle where Charcot is suspected. A normal film does not exclude it, and NG19 says to consider MRI if Charcot is still suspected (1.7.4). The same trap applies to bone infection: NG19 1.6.4 warns that osteomyelitis may be present despite normal inflammatory markers, X-rays and probe-to-bone testing, and 1.6.5 says to consider MRI where the initial X-ray does not confirm it
7. Send a soft tissue or bone sample from the base of the debrided wound (NG19 1.6.1). If you cannot obtain one in the ED, NG19 says take a deep swab rather than nothing - it still informs antibiotic choice. The thing to avoid is a superficial surface swab. Treat per local policy; antibiotic choice for a diabetic foot infection is not the same as for simple cellulitis
8. Document the ulcer site, size, depth, whether bone is probed, the pulses, and the temperature difference between feet, so that progression can be measured by whoever sees this patient next

Immediate referral to acute services for any limb-threatening or life-threatening problem, per NG19 1.4.1. Everything else active goes to the multidisciplinary foot care service within 1 working day. A painless ulcer in a well patient is still an active problem with a one-working-day clock on it - it is not a discharge-and-see-your-GP presentation.

• NICE NG19 - Diabetic foot problems: prevention and management
• NICE NG141 - Cellulitis and erysipelas: antimicrobial prescribing
• Lim HW et al. International Expert Consensus on Knowledge Gaps in Care for Dermatologic Disorders in Skin of Color. Int J Dermatol 2026
• Mukwende M, Tamony P, Turner M. Mind the Gap: A handbook of clinical signs in Black and Brown skin. St George’s, University of London (2020)