PUBLIC LIBRARY / CALCULATOR

PASI (Psoriasis Area and Severity Index)

Measures plaque psoriasis severity by summing lesion intensity and extent in four body regions; also calculates treatment response.

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Check the population, units and version. The result shows the formula or classification; it does not make an automatic treatment decision.

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Method · Limits of application

PASI/Fredriksson-Pettersson 1978: 4 regions, 3 signs 0–4, area 0–6, total 0–72

PASI quantifies the extent and signs of psoriasis, but the total alone does not identify a diagnosis or treatment need. The original study involved severe generalized chronic psoriasis. Percentage response requires a comparable baseline assessment; weights, technique and interpretation must match the version.

Required fields: 0/16 completed

Complete all required fields. Optional fields are marked.

Head and neck: erythema required

Head and neck: induration (thickness) required

Head and neck: scaling required

Head and neck: affected regional area required

Upper limbs: erythema required

Upper limbs: induration (thickness) required

Upper limbs: scaling required

Upper limbs: affected regional area required

Trunk: erythema required

Trunk: induration (thickness) required

Trunk: scaling required

Trunk: affected regional area required

Lower limbs: erythema required

Lower limbs: induration (thickness) required

Lower limbs: scaling required

Lower limbs: affected regional area required

Baseline PASI (before treatment), to calculate response (optional)Numeric value · range 0.1–72

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Conditions of use

Check the population, units, inclusion and exclusion criteria, and version in the original source. A result alone does not establish a diagnosis, discharge decision or prescription.

Documented parameters

Head and neck: erythema
Head and neck: induration (thickness)
Head and neck: scaling
Head and neck: affected regional area
Upper limbs: erythema
Upper limbs: induration (thickness)
Upper limbs: scaling
Upper limbs: affected regional area
Trunk: erythema
Trunk: induration (thickness)
Trunk: scaling
Trunk: affected regional area
Lower limbs: erythema
Lower limbs: induration (thickness)
Lower limbs: scaling
Lower limbs: affected regional area
Baseline PASI (before treatment), to calculate response

4/4 reference cases checked. Numerical tests are not clinical validation.

Sources and documentation

Documented formula

Transcribed from the source or a recorded revision; this is not a clinical recommendation.

In each region: (erythema + induration + scaling, each 0 to 4) × area (0–6) × region weight. Weights: head 0.1; upper limbs 0.2; trunk 0.3; lower limbs 0.4. PASI = sum of four regions (0–72).

area: 0 = none; 1 = < 10%; 2 = 10–29%; 3 = 30–49%; 4 = 50–69%; 5 = 70–89%; 6 = 90–100% of the region.

References

Identifier: pasi

Original clinical content: Brazilian Portuguese.

Method version

PASI/Fredriksson-Pettersson 1978: 4 regions, 3 signs 0–4, area 0–6, total 0–72

pasi@native-2026-10-03+8fdba30f80a0

Source for the active edition

The bibliographic edition identifies the source. By itself, it proves neither full conformity of the formula nor clinical approval.

Synthetic cases checked (4)

Synthetic cases for checking the implementation, with no patient data.

Case 1

reference-001

Inputs

Head and neck: erythema: 2
Head and neck: induration (thickness): 2
Head and neck: scaling: 1
Head and neck: affected regional area: 2 · 10 to 29%
Trunk: erythema: 3
Trunk: induration (thickness): 2
Trunk: scaling: 2
Trunk: affected regional area: 3 · 30 to 49%
Upper limbs: erythema: 0
Upper limbs: induration (thickness): 0
Upper limbs: scaling: 0
Upper limbs: affected regional area: 0 · no lesion
Lower limbs: erythema: 0
Lower limbs: induration (thickness): 0
Lower limbs: scaling: 0
Lower limbs: affected regional area: 0 · no lesion

{
  "e_h": "2",
  "i_h": "2",
  "d_h": "1",
  "a_h": "2",
  "e_t": "3",
  "i_t": "2",
  "d_t": "2",
  "a_t": "3",
  "e_s": "0",
  "i_s": "0",
  "d_s": "0",
  "a_s": "0",
  "e_i": "0",
  "i_i": "0",
  "d_i": "0",
  "a_i": "0"
}

Expected result

{
  "pasi": 7.3
}

Actual result

{
  "pasi": 7.3,
  "melhora": null
}

Case 2

reference-002

Inputs

Head and neck: erythema: 3
Head and neck: induration (thickness): 3
Head and neck: scaling: 3
Head and neck: affected regional area: 4 · 50 to 69%
Upper limbs: erythema: 3
Upper limbs: induration (thickness): 3
Upper limbs: scaling: 3
Upper limbs: affected regional area: 4 · 50 to 69%
Trunk: erythema: 3
Trunk: induration (thickness): 3
Trunk: scaling: 3
Trunk: affected regional area: 4 · 50 to 69%
Lower limbs: erythema: 3
Lower limbs: induration (thickness): 3
Lower limbs: scaling: 3
Lower limbs: affected regional area: 4 · 50 to 69%

{
  "e_h": "3",
  "i_h": "3",
  "d_h": "3",
  "a_h": "4",
  "e_s": "3",
  "i_s": "3",
  "d_s": "3",
  "a_s": "4",
  "e_t": "3",
  "i_t": "3",
  "d_t": "3",
  "a_t": "4",
  "e_i": "3",
  "i_i": "3",
  "d_i": "3",
  "a_i": "4"
}

Expected result

{
  "pasi": 36
}

Actual result

{
  "pasi": 36,
  "melhora": null
}

Case 3

reference-003

Inputs

Head and neck: erythema: 2
Head and neck: induration (thickness): 2
Head and neck: scaling: 1
Head and neck: affected regional area: 2 · 10 to 29%
Trunk: erythema: 3
Trunk: induration (thickness): 2
Trunk: scaling: 2
Trunk: affected regional area: 3 · 30 to 49%
Upper limbs: erythema: 0
Upper limbs: induration (thickness): 0
Upper limbs: scaling: 0
Upper limbs: affected regional area: 0 · no lesion
Lower limbs: erythema: 0
Lower limbs: induration (thickness): 0
Lower limbs: scaling: 0
Lower limbs: affected regional area: 0 · no lesion
Baseline PASI (before treatment), to calculate response: 36

{
  "e_h": "2",
  "i_h": "2",
  "d_h": "1",
  "a_h": "2",
  "e_t": "3",
  "i_t": "2",
  "d_t": "2",
  "a_t": "3",
  "e_s": "0",
  "i_s": "0",
  "d_s": "0",
  "a_s": "0",
  "e_i": "0",
  "i_i": "0",
  "d_i": "0",
  "a_i": "0",
  "basal": 36
}

Expected result

{
  "pasi": 7.3,
  "melhora": 79.72
}

Actual result

{
  "pasi": 7.3,
  "melhora": 79.72222222222221
}

Case 4

reference-004

Inputs

Lower limbs: erythema: 3
Lower limbs: induration (thickness): 3
Lower limbs: scaling: 2
Lower limbs: affected regional area: 3 · 30 to 49%
Upper limbs: erythema: 1
Upper limbs: induration (thickness): 0
Upper limbs: scaling: 1
Upper limbs: affected regional area: 1 · less than 10%
Head and neck: erythema: 0
Head and neck: induration (thickness): 0
Head and neck: scaling: 0
Head and neck: affected regional area: 0 · no lesion
Trunk: erythema: 0
Trunk: induration (thickness): 0
Trunk: scaling: 0
Trunk: affected regional area: 0 · no lesion

{
  "e_i": "3",
  "i_i": "3",
  "d_i": "2",
  "a_i": "3",
  "e_s": "1",
  "i_s": "0",
  "d_s": "1",
  "a_s": "1",
  "e_h": "0",
  "i_h": "0",
  "d_h": "0",
  "a_h": "0",
  "e_t": "0",
  "i_t": "0",
  "d_t": "0",
  "a_t": "0"
}

Expected result

{
  "pasi": 10
}

Actual result

{
  "pasi": 10,
  "melhora": null
}

Code and reproducibility

This tool’s code on GitHub

Download code and tests

Sources, version and reproduction instructions

The code tests are technical checks. Clinical approval and professional translation review are recorded separately.

Relationship with cancer research

General context — relationship to be defined

A resource for general clinical contexts. This edition does not assign a specific oncological relationship; selecting it for a study requires a justified question, population and purpose.