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PASI score

Author: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, 2009.

A PASI score is a tool used to measure the severity and extent of psoriasis (Psoriasis Area and Severity Index). It takes a few minutes and experience to calculate it accurately.


A representative area of psoriasis is selected for each body region. The intensity of redness, thickness and scaling of the psoriasis is assessed as none (0), mild (1), moderate (2), severe (3) or very severe (4).

Intensity Absent Mild Moderate Severe Very severe
Redness red 0
Score 0
red 1
Score 1
red 2
Score 2
red 3
Score 3
red 4
Score 4
Thickness thick 0
Score 0
thick 1
Score 1
thick 2
Score 2
thick 3
Score 3
thick 4
Score 4
Scaling scale 0
Score 0
scale 1
Score 1
scale 2
Score 2
scale 3
Score 3
scale 4
Score 4
Psoriasis: severity scoring

Calculation for intensity

The three intensity scores are added up for each of the four body regions to give subtotals A1, A2, A3, A4.

Each subtotal is multiplied by the body surface area represented by that region.


The percentage area affected by psoriasis is evaluated in the four regions of the body. In each region, the area is expressed as nil (0), 1-9% (1), 10-29% (2), 30-49% (3), 50-69% (4), 70-89% (5) or 90-100% (6).

Calculations for area

Each of the body area scores is multiplied by the area affected.

Total score

The PASI score is C1 + C2 + C3 + C4.

Other assessments

The Cardiff Dermatology Life Quality Index is a simple 10-question validated questionnaire to assess the impact of a skin disease on the patient's life. The same team have devised a specific assessment for the quality of life in psoriasis, the Psoriasis Disability Index.

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