Workup for Red Feet
Begin with a focused clinical assessment to distinguish between diabetic foot infection, peripheral arterial disease, erythromelalgia, and other inflammatory conditions—the presence of warmth, purulent discharge, or systemic signs (fever, tachycardia, elevated WBC) indicates infection requiring urgent intervention, while bilateral burning pain relieved by cooling suggests erythromelalgia.
Initial Clinical Assessment
Key Historical Features to Elicit:
- Diabetes status and duration (>10 years increases risk) 1
- Pain characteristics: Burning pain relieved by cooling suggests erythromelalgia 2, 3; pain with walking suggests claudication 1
- Timing: Acute onset (<2 days) versus chronic/episodic
- Triggers: Heat exposure, exercise (erythromelalgia) 3
- Systemic symptoms: Fever, chills (infection) 4, 5
- Smoking history and cardiovascular risk factors 1
Critical Physical Examination Elements:
For infection assessment 5:
- Measure erythema extent (>2 cm from wound = moderate infection)
- Check for purulent discharge, warmth, tenderness, induration
- Perform probe-to-bone test if ulcer present (positive test in high-risk patient is diagnostic for osteomyelitis) 5
- Assess pedal pulses bilaterally 1
For vascular assessment 1:
- Palpate dorsalis pedis and posterior tibial pulses
- Look for dependent rubor, pallor on elevation
- Check capillary refill
For neuropathy 1:
- Test protective sensation with Semmes-Weinstein 5.07 (10-g) monofilament
- Assess for loss of sensation between toes and under metatarsal heads
Diagnostic Algorithm
If Diabetic Patient with Erythema:
Step 1: Rule out infection 5
- Clinical diagnosis requires ≥2 of: erythema >0.5 cm around wound, warmth, tenderness, swelling, purulent discharge
- Exclude other causes: trauma, gout, Charcot arthropathy, thrombosis
Step 2: Classify infection severity 4, 5:
- Mild: Erythema <2 cm, skin/subcutaneous only, no systemic signs
- Moderate: Erythema ≥2 cm or deeper structures involved, no systemic signs
- Severe: Any infection with SIRS (temp >38°C or <36°C, HR >90, RR >20, WBC >12,000 or <4,000)
Step 3: Order laboratory studies 4, 6:
- CBC with differential (WBC >12,000 suggests infection)
- ESR and CRP (markedly elevated suggests osteomyelitis) 5
- Blood glucose/HbA1c
- Blood cultures if systemic signs present 6
- Plain X-rays of foot (all non-superficial infections) to assess for osteomyelitis, gas, foreign body
- MRI if osteomyelitis suspected but X-ray negative or diagnosis unclear 4
- Ankle-brachial index (ABI) for PAD screening (many asymptomatic) 1
- Wound swab from base after debridement (not sinus tract)
- Bone biopsy if osteomyelitis suspected for definitive diagnosis and antibiotic sensitivities 4, 5
If Non-Diabetic or Bilateral Red Feet Without Infection Signs:
Consider erythromelalgia 2, 3, 8:
- Triad: burning pain, erythema, warmth in extremities
- Relieved by cooling (but never recommend ice application—causes gangrene) 2
- Triggered by heat, exercise
- Order CBC annually (association with myeloproliferative disorders) 8
Consider other diagnoses 9:
- Stasis dermatitis (chronic venous insufficiency)
- Contact dermatitis (acute or chronic)
- Superficial/deep vein thrombosis
- Gout (acute monoarticular)
Critical Management Pitfalls
Do not delay surgical consultation for severe infections, deep abscess, extensive gangrene, necrotizing infection, or compartment syndrome 4, 7
Do not treat uninfected ulcers with antibiotics 4—this is ineffective and promotes resistance
In erythromelalgia misdiagnosed as diabetic foot infection, ice application causes gangrene and amputation 2—use fans, elevation, avoid heat instead
Obtain urgent vascular surgery consultation if PAD with infection—revascularization timing is critical 4
Refer high-risk diabetic patients (loss of protective sensation, structural abnormalities, prior ulcer/amputation, smoking) to foot care specialists for ongoing surveillance 1