Dermatology and Wound Care Calculators

The Psoriasis Area and Severity Index (PASI) scores erythema, induration, and desquamation (each 0–4) across four body regions (head, trunk, upper limbs, lower limbs), weighted by affected surface area. PASI ranges from 0 to 72. Mild psoriasis: PASI <10; moderate: 10–20; severe: >20. Biologic therapy eligibility typically requires PASI >10 with inadequate response to conventional therapy. Treatment response targets are PASI 75 (75% reduction), PASI 90, or PASI 100 — increasingly, PASI 90 is the benchmark for biologic therapies.

The Dermatology Life Quality Index (DLQI) is a 10-item patient-reported outcome measuring the impact of skin disease on quality of life over the past week (score 0–30). Interpretation: 0–1 = no effect; 2–5 = small effect; 6–10 = moderate effect; 11–20 = very large effect; 21–30 = extremely large effect. DLQI ≥10 is commonly used as a threshold for biologic eligibility in psoriasis alongside PASI. It is also validated for eczema, acne, urticaria, and other chronic dermatoses.

The ABCDE mnemonic helps identify suspicious pigmented lesions: Asymmetry (one half unlike the other), Border irregularity (ragged, notched, or blurred edges), Color variation (multiple shades of brown, black, red, white, or blue), Diameter >6 mm (though melanomas can be smaller), and Evolution (any change in size, shape, color, or new symptom). The 'E' (evolution) is often the most clinically significant — any changing lesion warrants dermatological evaluation regardless of other features. Dermoscopy significantly improves diagnostic accuracy over visual inspection alone.

The Rule of Nines divides the adult body into regions each representing ~9% TBSA: head and neck 9%, each arm 9%, chest 9%, abdomen 9%, upper back 9%, lower back 9%, each thigh 9%, each lower leg 9%, perineum 1%. It is fast and practical for initial triage. The Lund-Browder chart is more accurate, especially in children, as it adjusts for age-dependent surface area differences (the head is proportionally larger in children). For resuscitation calculations, Lund-Browder is preferred when time allows.

The Parkland formula calculates fluid requirements for burns involving ≥20% TBSA in adults (≥15–20% in children): 4 mL × weight(kg) × %TBSA burned of Lactated Ringer's in the first 24 hours. Half is given in the first 8 hours from the time of burn (not from arrival), the remainder over 16 hours. Target urine output 0.5–1 mL/kg/hr guides titration. Modern practice often uses the modified Brooke formula (2 mL/kg/%TBSA) to reduce over-resuscitation and abdominal compartment syndrome risk.

Body surface area is used to dose systemic treatments for extensive skin disease, including methotrexate for psoriasis (typically 7.5–25 mg/week, not BSA-based but monitored against body size), and some phototherapy dosing protocols. Topical steroid safety limits reference BSA: fingertip unit (FTU) guidelines indicate ~2 FTU covers an area equivalent to two palms (~2% BSA). For biologic dosing, most agents use fixed or weight-based dosing rather than BSA, though BSA-adjusted PASI is central to treatment decisions.