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What is a PASI Score?


Updated June 10, 2014

Question: What is a PASI Score?
When reading about a new treatment, the results in the form of the PASI score are often quoted. What does this mean?

The PASI score stands for Psoriasis Area and Severity Index. This tool allows researchers to put an objective number on what would otherwise be a very subjective idea: how bad is a person's psoriasis. To make up the score, the three features of a psoriatic plaque (redness) scaling and thickness are each assigned a number from 0 to 4 with 4 being worst. Then the extent of involvement of each region of the body is scored from 0 to 6. Adding up the scores give a range of 0 to 72.

Many studies quote the improvement seen in the PASI score over time as a measure of a drug's effectiveness. For example, they may note that a certain proportion of patients experienced a 75% reduction in their PASI scores over a 12-week treatment period and report this as a percentage of people achieving "PASI 75."

PASI scores are seldom used in clinical practice, although more fastidious doctors or those working at university-based clinics or specialized psoriasis treatment centers may routinely use this tool to follow their patients' progress.


BMJ Clinical Evidence.

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