What is the role of Sweat Patch Test (SPT) and distinguishing between superficial and deep partial thickness burns (DPT) in the diagnosis and management of burns?

Burn Depth Assessment: SPT and DPT Diagnosis

The Sweat Patch Test (SPT) is not a recognized or recommended diagnostic tool in modern burn assessment, and distinguishing superficial from deep partial thickness (DPT) burns should rely on clinical evaluation supplemented by laser Doppler imaging when available, as clinical assessment alone is accurate in only 60-75% of cases. 1

Primary Assessment Methods

Clinical Evaluation

• Clinical examination remains the most frequent technique for assessing burn depth, though it has significant limitations with accuracy rates of only 60-75% even when performed by experienced burn surgeons 1
• Burn depth should be categorized as superficial, partial thickness, or full thickness to guide management 2
• Deep partial thickness burns require differentiation from superficial partial thickness because they often require surgical excision and grafting to prevent hypertrophic scarring, while superficial burns heal by re-epithelialization with minimal scarring 3

Objective Diagnostic Modalities

• Laser Doppler imaging (LDI) is the only technique with substantial evidence demonstrating accurate prediction of wound outcome and has FDA approval for burn depth assessment 1
• LDI and indocyanine green (ICG) video angiography offer the best data-supported estimates of accuracy among available modalities 3
• For initial emergency assessment, telemetry and simple burn photographs are the best options 1

Clinical Indicators of Burn Depth

Deep Partial or Full Thickness Burns

• Blue, purple, or pale extremities indicate poor perfusion and deep injury requiring emergency intervention 4
• Hand burns with blanched skin falling off fingers indicate deep partial- or full-thickness injury requiring immediate specialist referral 4
• Deep burns in function-sensitive areas (face, hands, feet, perineum, flexure lines) require burn center evaluation regardless of size 5, 4

Assessment Timing

• Burn depth assessment must be repeated during initial management as wounds can progress and initial estimates are often inaccurate 5, 6
• Without timely intervention, superficial burns can convert to deeper wounds 3

Common Pitfalls to Avoid

• Do not rely solely on clinical examination for depth assessment, as this leads to misclassification in 25-40% of cases 1
• Do not delay specialist consultation when burn depth is uncertain, as telemedicine can reliably improve depth characterization 5
• Avoid waiting for definitive signs of compartment syndrome (such as pulse loss) in suspected deep circular burns, as irreversible damage occurs within 6-8 hours 4
• Do not assume that erythema alone indicates burn depth—actual tissue damage and perfusion are more important prognostic indicators 6

Recommended Diagnostic Algorithm

1. Perform initial clinical assessment of burn depth using visual inspection and palpation 2
2. Consult burn specialist early, ideally through telemedicine if direct consultation unavailable, particularly when depth assessment is uncertain 5, 2
3. Consider laser Doppler imaging for treatment decisions when available, as it provides the most accurate objective assessment 1
4. Reassess burn depth serially during the first 24-48 hours, as initial assessments frequently change 5
5. Refer to burn center any deep burns >5% TBSA in adults or children, or any deep burns in function-sensitive areas regardless of size 5, 2