Burn severity classification

Overview

Burn severity classification stratifies injuries by their anticipated clinical impact to guide disposition (outpatient, inpatient, burn center), treatment intensity, and prognostication. The American Burn Association classifies burns as minor, moderate, or major based on the integration of burn depth, total body surface area (TBSA) burned, anatomic location, patient age, mechanism, and comorbidities ^[1][2]. Accurate severity classification is the bridge between initial assessment and definitive management planning.

Classification Framework

Burn Depth Classification

The modern classification system grades burns by increasing depth ^[3][4]:

• Superficial (first degree): Involves epidermis only. Presents with erythema, pain, no blistering. Heals within 7 days without scarring. Sunburn is the prototypical example. Not included in TBSA calculations for resuscitation.
• Superficial partial thickness (second degree): Extends into the papillary dermis. Presents with blistering, moist wound surface, severe pain, intact sensation. Heals within 14 to 21 days with minimal scarring if no infection occurs.
• Deep partial thickness (second degree): Extends into the reticular dermis, destroying most dermal appendages. Presents with mixed red and white coloration, reduced sensation, sluggish capillary refill. May heal in 3 to 9 weeks with significant scarring, but often requires excision and grafting for optimal outcomes.
• Full thickness (third degree): Destroys the entire dermis. Presents as waxy white, leathery, or charred, insensate, no capillary refill. Requires excision and grafting as spontaneous re-epithelialization cannot occur from dermal appendages ^[3][4].
• Fourth degree: Extends beyond the dermis into subcutaneous tissue, fascia, muscle, or bone. Associated with electrical injury and prolonged contact burns.

ABA Severity Classification

The ABA classifies burns into three categories based on TBSA, depth, location, and patient factors ^[1][2]:

Minor burns:

• Under 10% TBSA partial thickness in adults (under 5% in children or elderly)
• Under 2% TBSA full thickness
• No involvement of critical areas (face, hands, feet, genitalia, perineum, major joints)
• No inhalation injury, electrical injury, or significant comorbidities
• Suitable for outpatient management

Moderate burns:

• 10% to 20% TBSA partial thickness in adults (5% to 10% in children or elderly)
• 2% to 5% TBSA full thickness
• No critical area involvement, no inhalation injury
• Require inpatient care but not necessarily burn center admission

Major burns:

• Over 20% TBSA partial thickness (over 10% in children or elderly)
• Over 5% TBSA full thickness
• Burns involving critical areas
• Inhalation injury, electrical injury, chemical burns
• Burns with significant comorbidities or concomitant trauma
• Require burn center care

Prognostic Severity Scoring

Baux Score and Modified Baux Score

The Baux score (age + %TBSA) provides a rapid mortality estimate. The modified Baux score adds 17 points for inhalation injury. While simple, these scores do not account for comorbidities, burn depth distribution, or quality of care ^[2]. Kumar demonstrated that serial serum protein measurements and albumin/globulin ratio changes correlate with burn severity and mortality, with total protein values below 5.0 g/dL associated with 95% mortality ^[5].

ABSI (Abbreviated Burn Severity Index)

The ABSI incorporates age, sex, TBSA, presence of full-thickness burn, and presence of inhalation injury into a composite severity score. It assigns point values to each variable and stratifies patients by predicted mortality probability ^[2].

Objective Severity Assessment

Imaging-Based Classification

Rowland et al. demonstrated that spatial frequency-domain imaging combined with machine learning can predict burn severity at 24 hours with 92.5% to 94.4% accuracy in a porcine model ^[6]. These approaches aim to remove the subjectivity inherent in clinical depth and severity assessment.

Laser Doppler Imaging

Laser Doppler imaging remains the most validated adjunct for differentiating superficial partial thickness from deep partial thickness burns, which is the critical distinction that determines whether a burn will heal within 21 days without surgery ^[7].

Special Considerations

Pediatric Severity

Children have proportionally larger body surface area relative to body mass, making them more susceptible to systemic effects at lower absolute burn sizes. TBSA thresholds for severity classification are lower in children (and the elderly) for this reason ^[1][3]. The Lund-Browder chart is essential for accurate pediatric TBSA assessment.

Inhalation Injury

The presence of inhalation injury independently increases mortality and escalates severity classification regardless of TBSA. It adds approximately 17 percentage points to the modified Baux score and is an absolute indication for burn center referral ^[2][8].

Deep Burns and Surgical Need

In deep second-degree and higher-grade burns, the epidermis and skin appendages are destroyed so that healing occurs only with severe scarring. Necrectomy and skin grafting are recommended for these injuries ^[9]. Extensive and deep burns should be treated at specialized centers per established guidelines.

Controversies and Evidence Gaps

The ABA severity classification relies on expert consensus rather than prospective outcome data correlating classification category with patient outcomes ^[2]. Clinical depth assessment alone misclassifies approximately 25% of indeterminate-depth burns. The threshold TBSA at which burn center care demonstrably improves outcomes over non-burn-center care is not precisely defined. Machine learning and advanced imaging tools for severity classification remain in preclinical or early clinical validation stages ^[6]. Whether adding biomarkers (serum protein, inflammatory markers) to clinical severity scores improves prognostic accuracy has not been prospectively validated in large cohorts ^[5].

References

[1] Morgan ED, Bledsoe SC, Barker J (2000). Ambulatory management of burns. Am Fam Physician. 62(9):2015-26. PMID: 11087185 [2] Harvey JS, Watkins GM, Sherman RT (1984). Emergent burn care. South Med J. 77(2):204-14. PMID: 6367073 [3] Vaughn L, Beckel N (2012). Severe burn injury, burn shock, and smoke inhalation injury in small animals. Part 1: burn classification and pathophysiology. J Vet Emerg Crit Care. 22(2):179-86. PMID: 23016809 [4] Bezuhly M, Fish JS (2012). Acute burn care. Plast Reconstr Surg. 130(2):349e-358e. PMID: 22842431 [5] Kumar P (2010). Grading of severity of the condition in burn patients by serum protein and albumin/globulin studies. Ann Plast Surg. 65(1):74-9. PMID: 20548219 [6] Rowland R et al. (2019). Burn wound classification model using spatial frequency-domain imaging and machine learning. J Biomed Opt. 24(5):1-9. PMID: 31134769 [7] [Cross-reference: burn-depth-assessment — Laser Doppler imaging section] [8] Fisher JC, Wells JA, Fulwider BT, Edgerton MT (1977). Do we need a burn severity grading system. J Trauma. 17(3):252-5. PMID: 850285 [9] Daigeler A, Kapalschinski N, Lehnhardt M (2015). Therapy of burns. Chirurg. 86(4):389-401. PMID: 25894015