REASONING GP · Clinical algorithm · Quick reference

Leg ulcers in adults — triage and diagnostic approach

Daytime GP, OOH and community nursing. Exclude the limb-threatening causes, measure the ABPI before any compression, then classify the ulcer. Ongoing compression, wound care and recurrence prevention are in the full Steps pathway.
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AdultsGP + communityABPI firstv1.0 · Sep 2026
Core rule. Never apply compression before the ABPI is measured in both legs. Full compression on an ischaemic limb causes tissue necrosis and is a recognised cause of avoidable amputation. ABPI 0.8–1.3 permits full compression; below 0.8 or above 1.3 the patient is referred first. Any ulcer on the foot of a person with diabetes goes to the multidisciplinary foot service within one working day (NG19) and is not managed in general practice. A venous-looking leg does not exclude arterial disease.
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Before any wound-care decision: is this an emergency now? Stop and escalate if any of these is present
Pain out of proportion to the appearance, crepitus, dusky or blistering skin, rapidly advancing erythema, systemic toxicity → necrotising fasciitis, 999 · sepsis features or NEWS2 ≥5 → same-day admission · pale, cold, pulseless painful foot, or rest pain relieved by hanging the leg out of bed → critical or acute limb ischaemia, same-day vascular · exposed bone or probe-to-bone → osteomyelitis, same-day · any new diabetic foot ulcer → foot service within 24 hours. Do not debride, do not compress, and do not start a dressing regimen before these are excluded.
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Define the ulcer in four lines Enough to place the patient in the table below

Time

Duration, how it started (spontaneous, minor knock, bite, scratch), previous ulcers on either leg and how they were treated, cycles of healing and breakdown. Baseline size measured or traced today — the 4-week and 12-week rules depend on it.

Character

Site, size, depth, edge, base tissue, exudate, odour. Pain and position: venous aches and is better on elevation; arterial is worse at night and worse on elevation, relieved by dangling; neuropathic is painless. A patient who sleeps in a chair has arterial disease until proven otherwise.

Context

Venous: previous DVT, varicose veins or vein surgery, leg fracture, pregnancy, obesity, prolonged standing. Arterial: smoking, diabetes, hypertension, lipids, claudication distance, known vascular disease. Also: IBD or rheumatoid arthritis, sickle cell, injecting drug use, previous radiotherapy, steroids or immunosuppressants, nicorandil and hydroxycarbamide.

Associated

Oedema and its cause (heart, renal, liver, lymphoedema, calcium channel blocker, immobility) · fever or spreading redness · sensory loss · purpura, livedo or multiple ulcers (vasculitis) · who does the dressings, and whether the patient can see and reach their own feet.
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Red-flag screen: trigger → concern → destination → what to do before handover One row is enough; do not add up reassuring features
Trigger / red flagLeading concern · destinationDo now · do not delay
Pain out of proportion, crepitus, dusky or blistering skin, rapidly spreading erythema, systemic toxicity. Necrotising fasciitis
999 now		 ABCDE, observations, mark the erythema edge with the time. Nil by mouth. Do not wait for a swab, an antibiotic response or a surgical opinion by letter.
Rest pain (worse at night, eased by dependency), pale cold foot, absent pulses, gangrene, or ABPI <0.5 with tissue loss. Critical or acute limb ischaemia
Same-day vascular 999 if acute — the six Ps		 Remove any compression immediately. Keep the limb warm, dependent and protected; give adequate analgesia. Do not elevate an ischaemic leg. Record pulses, ABPI if already known, and smoking and diabetes status.
Any new ulcer on the foot of a person with diabetes, or suspected infection, gangrene, Charcot deformity or osteomyelitis in a diabetic foot. Diabetic foot ulcer
Multidisciplinary foot service within 1 working day · NICE NG19		 Do not manage in general practice. The foot is painless, so it deteriorates unnoticed; around 80% of diabetes-related amputations are preceded by an ulcer. Probe-to-bone suggests osteomyelitis. Offload, do not compress, and refer today.
Fever, rigors, spreading erythema, purulence, increasing pain or NEWS2 elevated in a person with an ulcer. Cellulitis · osteomyelitis · sepsis
Same-day admission if systemically unwell Oral antibiotic if well		 Infection is a clinical diagnosis: increasing pain, spreading erythema, purulence, systemic upset. Odour and exudate alone are not infection. Swab only once that clinical decision is made, to guide the agent. Mark and date the erythema edge.
Ulcer not healed after 12 weeks of appropriate treatment; rolled or everted edge; exuberant friable granulation; bleeding; rapid change; atypical site; an ulcer arising in an old scar, burn or chronic wound. Squamous cell carcinoma, including Marjolin's ulcer · BCC · melanoma
Urgent suspected skin cancer referral / incisional biopsy · NICE NG12		 Biopsy the raised edge, not the necrotic centre, or the sample is non-diagnostic. Malignant transformation is routinely mistaken for granulation tissue for months. Book the 12-week review at the first appointment — that is what makes this rule work.
An associated soft-tissue lump that is enlarging, painful or deep to fascia. Soft-tissue sarcoma
Urgent direct-access ultrasound within 2 weeks · NICE NG12		 State the size, depth and rate of growth in the request. Do not excise or biopsy a suspected sarcoma in primary care.
Atypical ulcer. Rapidly enlarging and painful with a violaceous, undermined edge, often with IBD or rheumatoid arthritis. Or purpura, livedo, multiple ulcers with systemic symptoms; or a painful black eschar in a hypertensive diabetic or a patient with renal failure. Pyoderma gangrenosum · vasculitis · cryoglobulinaemia · calciphylaxis · Martorell's hypertensive ulcer
Urgent dermatology / rheumatology		 Do not debride — pathergy makes pyoderma gangrenosum worse, and debridement is the reflex that causes the harm. Do not compress hard; avoid unnecessary antibiotics — treatment is immunosuppression. Urinalysis for blood and protein, FBC, U&Es, CRP, ANCA and ANA. These ulcers do not respond to compression and dressings, and delay costs tissue.
ABPI <0.8 or >1.3, or mixed arteriovenous features, in a leg that otherwise looks venous. Unrecognised arterial disease
Vascular assessment before any compression		 Measure both legs, supine and rested 10–20 minutes, using the highest brachial pressure as the denominator. A high ABPI is not reassurance — medial calcification in diabetes and CKD makes the vessel incompressible, so >1.3 needs toe-brachial pressures or duplex. Reduced compression is a specialist decision only.
Safety rule. New or increasing pain under a compression bandage, or new numbness, means remove the bandage and reassess the same day — it is the presentation of pressure damage on an under-recognised ischaemic limb, not expected discomfort. Palpable pulses do not exclude significant arterial disease, and a normal-looking venous leg can have an ABPI of 0.6. Repeat the ABPI every 6 months: arterial disease progresses.
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Focused examination and investigation Both legs, shoes and socks off; remote assessment cannot complete this and is an escalation criterion

Observations

Temperature, pulse, BP, RR, NEWS2 if unwell; BMI; blood glucose or HbA1c. Ulcers are frequently bilateral, and a second ulcer changes the diagnosis.

System examination

Ulcer: site, measured size or tracing, depth, edge, base, exudate, odour, exposed tendon or bone. Surrounding skin: oedema, varicose eczema, haemosiderin staining, lipodermatosclerosis, atrophie blanche, cellulitis, maceration. Mobility and ankle range of movement.

Targeted signs

Posterior tibial, dorsalis pedis, popliteal and femoral pulses in both legs. 10 g monofilament at 10 sites, vibration, ankle reflexes. Callus, deformity, interdigital fungal infection, nail disease, temperature asymmetry (Charcot), and a look inside the shoe for foreign bodies. Whole-skin survey.

Investigations

Doppler ABPI in both legs — before any compression. Bloods: FBC, HbA1c, U&Es, LFTs, CRP, ferritin and albumin, lipids; ANCA, ANA, rheumatoid factor and cryoglobulins if vasculitis is suspected; urinalysis. Swab only if clinically infected. Not from primary care: duplex and arterial imaging (vascular-led), MRI for osteomyelitis. Consider patch testing for persistent peri-ulcer eczema.
Colour is semantic: red = emergency now · amber = same-day acute assessment · blue = define/assess · green = benign diagnosis established · purple = uncertain / specialist route. Continued on page 2: classification, ulcer classifier, routine referral, primary-care treatment, endpoint.
REASONING GP · Leg ulcers in adults — triage and diagnostic approach
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Classify: three exits, not two A "venous ulcer" without an ABPI is an unclassified ulcer

Limb- or life-threatening

Ischaemia, necrotising or systemic infection, osteomyelitis, a diabetic foot ulcer, or suspected malignancy. Output: name the concern, use the destination above, remove any compression, and hand over pulses, ABPI if known, and diabetes and smoking status.

Venous ulcer established

Medial gaiter site, typical surrounding skin changes, pulses present and ABPI 0.8–1.3, no diabetic foot involvement, no atypical features. Output: record ABPI with its date and the baseline size; start full compression with community nursing and refer to a vascular service.

Unclassified / uncertain

ABPI not yet measured or unreliable (>1.3), mixed features, atypical site or edge, multiple ulcers, or no progress on treatment. Output: do not compress and do not label venous. State what is outstanding and who arranges it by when.
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Ulcer classifier — site, appearance, pulses, ABPI Site and pain identify the type in most cases before any equipment
Venous (60–70%)Medial gaiter area above the malleolus; shallow, irregular sloping edge, granulating, heavily exudative; oedema, varicose eczema, haemosiderin staining, lipodermatosclerosis, atrophie blanche; pulses present; ABPI 0.8–1.3. Aches, better on elevation.
Arterial (10–15%)Lateral malleolus, shin, toes or pressure points; deep, punched-out, sharply demarcated, pale or necrotic dry base; cold shiny hairless skin, absent pulses, dependent rubor; ABPI <0.8. Worse at night and on elevation. Do not compress.
Mixed arteriovenous (10–15%)Features of both, ABPI 0.5–0.8. Common in older patients and in diabetes. Needs vascular assessment; reduced compression only under specialist supervision, never on GP initiative.
Neuropathic / diabetic footPlantar surface, metatarsal heads, heel, or under callus; painless, punched-out with surrounding hyperkeratosis; warm foot, palpable pulses, absent monofilament sensation; Charcot deformity. Foot service within 1 working day.
Malignant and inflammatorySCC (including Marjolin's in chronic ulceration), BCC, melanoma, cutaneous lymphoma — rolled or everted edge, exuberant granulation, no healing at 12 weeks. Pyoderma gangrenosum, vasculitis, rheumatoid ulcers, necrobiosis lipoidica, calciphylaxis.
Do not label by default"Venous" without an ABPI, and "infected" on odour alone, are not diagnoses. Also consider: pressure ulcer (and whether a safeguarding referral is needed), sickle cell ulceration, nicorandil- or hydroxycarbamide-induced ulceration (resolves on withdrawal — check the repeat list), trauma or burn, factitious, and tropical or mycobacterial infection with relevant travel.
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Refer routinely from this consultation Not same-day, not 999 — the cases that leave by letter
Vascular service — CG168: refer everyone with a venous leg ulcer, or one healed within the past 12 months, for duplex assessment and consideration of endovenous treatment of superficial reflux; correcting the incompetence substantially reduces recurrence, and this is the most under-made referral in leg ulcer care. Routine dermatology: atypical or non-healing ulcer needing biopsy, and persistent peri-ulcer eczema for patch testing (contact allergy to dressings, adhesives, lanolin and topical antibiotics is common). Tissue viability and community nursing: compression initiation and maintenance, debridement, complex exudate, pressure redistribution, hosiery fitting. Interim advice: elevate above hip level, ankle exercises hourly, emollient daily, and the written safety-net below. Not routine: ABPI <0.8 or >1.3, any diabetic foot ulcer, suspected malignancy at 12 weeks, and every page-1 red flag.
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The only treatment decisions that belong in this consultation Everything else is in the management pathway
Ischaemia, necrotising infection, sepsis, diabetic foot ulcerReferral is the treatment. Remove any compression from an ischaemic or painful limb. Keep an ischaemic leg warm, dependent and protected; do not elevate it. Do not debride a suspected pyoderma gangrenosum or an ischaemic ulcer. No dressing regimen substitutes for the referral.
Clinically infected ulcer, systemically wellFlucloxacillin 500 mg–1 g four times daily for 7 days (clarithromycin 500 mg twice daily if penicillin-allergic), per NG141. Swab to guide if not responding. Only for clinical infection — all chronic ulcers are colonised, and swabbing an uninfected ulcer generates antibiotics that do not help healing and do drive resistance and C. difficile.
Venous ulcer, ABPI 0.8–1.3Strong graduated multilayer compression, approximately 40 mmHg at the ankle, applied by a trained practitioner (four-layer, two-layer or wrap system) — this, not the dressing, heals the ulcer. Under-dosing because of discomfort is the commonest reversible cause of non-healing: persist with good analgesia. Simple non-adherent dressing chosen by exudate level; no antimicrobial dressing without clinical infection.
Pain and oedema todayParacetamol with or without a topical or oral NSAID; time analgesia to dressing changes; topical local anaesthetic before debridement. Ischaemic rest pain often needs an opioid and urgent vascular input. Neuropathic pain: amitriptyline, duloxetine, gabapentin or pregabalin (CG173). Elevate above hip level, hourly ankle exercises, and review calcium channel blockers and other oedema-causing drugs.
Peri-ulcer eczemaShort course of a moderate-potency topical corticosteroid to the eczematous skin only, not the ulcer bed, plus generous emollient. Avoid topical antibiotics and lanolin-containing products — neomycin and framycetin are potent sensitisers and a common iatrogenic cause of persistent peri-ulcer dermatitis.
Where arterial disease is foundThe ulcer is a marker of widespread atherosclerosis: high-intensity statin, antiplatelet, BP control, smoking cessation referral, supervised exercise programme. This does more for life expectancy than any dressing. Optimise glycaemic control in diabetes; screen nutrition with MUST and correct protein, vitamin C, zinc and iron deficiency.
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Endpoint and documentation Finish with one of four conclusions and a named owner

1 · Limb- or life-threatening

999, same-day vascular or foot-service route taken; pulses, ABPI if known, compression removed and when, observations, diabetes and smoking status, analgesia given.

2 · Serious cause possible

Same-day or urgent route arranged; state what is being excluded, who was spoken to, and the deadline. Erythema edge marked and dated; biopsy or imaging requested by name.

3 · Venous ulcer established

ABPI value and date, baseline measurement and dated photograph with a scale, compression class and who applies it, vascular referral made, 4-week and 12-week review dates booked, hosiery plan after healing.

4 · Unclassified

ABPI outstanding or unreliable: compression withheld, the reason recorded, who will measure it and when, interim wound care and analgesia, and explicit escalation criteria.
Why a venous diagnosis is safe today, in one line: ABPI 0.8–1.3 measured in both legs today · typical medial gaiter site with venous skin changes and pulses present · not a diabetic foot · no atypical edge, and a 12-week biopsy review booked · baseline size recorded and a ≥30% area reduction expected by 4 weeks · written safety-net given. Safety-net wording: call 999 if the pain becomes far worse than the wound looks, the skin turns dusky or crackles, or you become feverish and very unwell; remove the bandage and contact us the same day if the pain increases under it, your toes go numb, cold or pale, the redness spreads, the discharge becomes pus-like, or the ulcer suddenly gets bigger.
OOH / remote limitation. This presentation cannot be completed remotely: an ABPI, pulses, monofilament testing and direct inspection of both feet — including between the toes and inside the shoes — are all required. Convert to face-to-face if the ulcer cannot be seen and measured; the patient has diabetes, is anticoagulated or is immunosuppressed; there is new pain under a bandage; or district nursing and timely review cannot be arranged. Under time pressure the default is the safer destination.
Clinical decision support only; follow local vascular, diabetic foot and referral policies and check doses against the current BNF. Source hierarchy: NICE guidelines first, then BNF/MHRA for doses and safety, then national specialty guidance. Sources: NICE CG168 Varicose veins in the legs · NG19 Diabetic foot problems: prevention and management · NG12 Suspected cancer: recognition and referral · NG141 Cellulitis and erysipelas: antimicrobial prescribing · CG173 Neuropathic pain in adults · NG51 Sepsis · NICE guidance — Leg ulcer — venous · SIGN 120 Management of chronic venous leg ulcers · National Wound Care Strategy Programme lower limb recommendations · BNF. Review after any guidance or medicines-safety update, otherwise every 6 months. © Reasoning GP · gpreasoning.uk