PASI Calculator

Psoriasis Area and Severity Index — Fredriksson & Pettersson, 1978

Purpose
Physician-assessed severity of plaque psoriasis combining sign intensity (erythema, induration, desquamation) and extent in four body regions.
Population
Adults and children with plaque psoriasis. Reference outcome in clinical trials and in biologic eligibility criteria. Less sensitive in limited disease (BSA < 10%).
Formula
PASI = 0.1·(E+I+D)·Ahead + 0.2·(E+I+D)·Aupper limbs + 0.3·(E+I+D)·Atrunk + 0.4·(E+I+D)·Alower limbs · Range 0–72
Severity thresholds
European consensus (Mrowietz 2011): mild = PASI ≤ 10 (with BSA ≤ 10 and DLQI ≤ 10) · moderate-to-severe = PASI > 10 or BSA > 10, with DLQI > 10. Rule of Tens (Finlay 2005): BSA > 10 or PASI > 10 or DLQI > 10 = current severe psoriasis.
📈 PASI response (PASI 50 / 75 / 90 / 100)

Enter the baseline PASI (before treatment). The current PASI is filled in automatically after calculating above, but can be edited.

Improvement from baseline (ΔPASI) —
PASI 50Not reached
PASI 75Not reached
PASI 90Not reached
PASI 100Not reached
🎯 Treatment goals (Mrowietz 2011): ΔPASI ≥ 75 = goal reached · ΔPASI 50 to < 75 with DLQI ≤ 5 = acceptable, with DLQI > 5 = modify treatment · ΔPASI < 50 = modify treatment.
✋ BSA estimate and Rule of Tens

The patient's whole palm (palm plus fingers) ≈ 1% of body surface area. Count the number of palms needed to cover all plaques.

Rule of Tens (Finlay 2005) —
💡 Current severe psoriasis if BSA > 10% or PASI > 10 or DLQI > 10. The European consensus (Mrowietz 2011) defines moderate-to-severe psoriasis as (BSA > 10 or PASI > 10) and DLQI > 10, and lists upgrade criteria (involvement of visible areas, scalp, genitals, palms/soles, nails, pruritus with scratching, recalcitrant plaques) that can reclassify mild disease as moderate-to-severe.
📚 References
  1. Fredriksson T, Pettersson U. Severe psoriasis — oral therapy with a new retinoid. Dermatologica. 1978;157(4):238–44.
  2. Mrowietz U, Kragballe K, Reich K, et al. Definition of treatment goals for moderate to severe psoriasis: a European consensus. Arch Dermatol Res. 2011;303(1):1–10.
  3. Finlay AY. Current severe psoriasis and the Rule of Tens. Br J Dermatol. 2005;152(5):861–7.
  4. Feldman SR, Krueger GG. Psoriasis assessment tools in clinical trials. Ann Rheum Dis. 2005;64(Suppl 2):ii65–8.
  5. Nast A, Smith C, Spuls PI, et al. EuroGuiDerm Guideline on the systemic treatment of psoriasis vulgaris — Part 1: treatment and monitoring recommendations. J Eur Acad Dermatol Venereol. 2020;34(11):2461–98.
Clinical decision support only. This tool is intended to assist clinical assessment and does not replace professional judgment. Always interpret results in the context of the individual patient.