Psoriasis Australia

How is psoriasis diagnosed?

eing given a formal diagnosis is an important step in determining the most suitable treatment option available to you. There are often many other skin conditions that can be mistaken for psoriasis. Your doctor can make a diagnosis and then help you treat the condition with the right medications.

It is highly recommended that if your GP does diagnose you with psoriasis that you ask to be referred to a dermatologist for more specialised care.

Psoriasis tends to have periods when it flares up and you will experience more symptoms, while at other times it may seem to be dormant and hence you will notice fewer symptoms. Unfortunately, there is no cure by psoriasis, but there are many different type of medications that can be used to treat your psoriasis that will allow you to potentially have clear or near clear skin.

Your doctor will discuss your medical history and conduct a physical examination, focusing on your skin, nails and scalp. It is possible that further tests may be required such as a biopsy to assist with diagnosis.

Psoriasis Area and Severity Index (PASI)

The severity of your diagnosis is determined by the Psoriasis Area and Severity Index, know as PASI. This is a formal system used to measure the severity and extent of your psoriasis, before and after treatment. 

A PASI score is an objective measure of how much of the skin is covered by psoriasis plaques and also how red, thick and scaly the plaques are. The higher the PASI score, the greater the severity of your psoriasis.

Scoring System

The scoring system used to calculate the PASI rates the intensity of the psoriasis from none to very severe and estimating the percentage of the body that is covered by the lesions. A PASI Score can range from 0-72 indicating the following:

  • 0 to 5: None to mild Psoriasis
  • 6 to 10: moderate Psoriasis
  • 11 or above: severe Psoriasis 

How is the PASI score calculated?

The PASI is calculated using a complicated mathematical formula. It uses information acquired by a dermatologist during physical examination taking into account the regions the psoriasis is present on the body (area) and the intensity of the lesions.


Four different areas of the body are assessed as part of the PASI. These are scored individually and include:

  • Head and neck
  • Upper limbs
  • Trunk
  • Lower limbs
Each area is assessed for the percentage the psoriasis covers and is scaled as follows:
  • 0: No Psoriasis
  • 1: 1% to 9% of the area has Psoriasis present
  • 2: 10% to 29% of the area has Psoriasis present
  • 3: 30% to 49% of the area has Psoriasis present
  • 4: 50% to 69% of the area has Psoriasis present
  • 5: 70% to 89% of the area has Psoriasis present
  • 6: 90% to 100% of the area has Psoriasis present


In addition to the area