PASI (Psoriasis Area and Severity Index)
PASI (Fredriksson 1978): psoriasis severity — for each of four regions grade erythema/induration/desquamation 0–4 and enter % area.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Head / neck: erythema
- 2
- Head / neck: induration
- 2
- Head / neck: desquamation
- 2
- Head / neck: % area involved
- 25
- Upper limbs: erythema
- 1
- Upper limbs: induration
- 1
- Upper limbs: desquamation
- 1
- Upper limbs: % area involved
- 5
- Lower limbs: erythema
- 3
- Lower limbs: induration
- 3
The other 2 values
- Lower limbs: desquamation
- 3
- Lower limbs: % area involved
- 60
Result: PASI 16.2/72 — moderate psoriasis (10–20).
The tool opens with these values already filled in. Replace them with your own.
What the result means
- Bands
- mild < 10, moderate 10–20, severe > 20; PASI-75/90 (a 75% or 90% reduction from baseline) is the usual trial response endpoint.
What you enter
- Head / neck: erythema (0–4)
- Head / neck: induration (0–4)
- Head / neck: desquamation (0–4)
- Head / neck: % area involved (0–100)
- Upper limbs: erythema (0–4)
- Upper limbs: induration (0–4)
- Upper limbs: desquamation (0–4)
- Upper limbs: % area involved (0–100)
- Trunk: erythema (0–4)
- Trunk: induration (0–4)
The other 6 fields
- Trunk: desquamation (0–4)
- Trunk: % area involved (0–100)
- Lower limbs: erythema (0–4)
- Lower limbs: induration (0–4)
- Lower limbs: desquamation (0–4)
- Lower limbs: % area involved (0–100)
How this is calculated
- Formula
- PASI = Σ over four regions of (erythema + induration + desquamation, each 0–4) × area grade 0–6 × weight (head 0.1, upper 0.2, trunk 0.3, lower 0.4), range 0–72.
Fredriksson T, Pettersson U. Severe psoriasis — oral therapy with a new retinoid. Dermatologica. 1978;157(4):238-244. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.