palm of a hand

PASI Score: Understanding Your Psoriasis Severity

By Beth W. Orenstein
Reviewed by Allison Truong, M.D.
June 22, 2022

Is your psoriasis mild, moderate, or severe? Your doctor will want to make that distinction so they can give you the best treatment recommendations. They may also use your severity to explain to your insurance company why they’d like you to use a certain medication.

Dermatologists may use a number of different scales to classify psoriasis severity and discuss treatment options. The gold standard has long been the Psoriasis Area and Severity Index (PASI).

How Doctors Use the Psoriasis Area and Severity Index

The PASI is used often in doctors’ offices because many insurance companies require body surface area and PASI to be documented to approve certain medications, such as biologics. It’s also useful in clinical research, says Paul S. Yamauchi, M.D., a board-certified dermatologist at the Dermatology Institute & Skin Care Center, in Santa Monica, California, because PASI can be used to monitor the progression of disease and to evaluate the effectiveness of different medications.

Frank Morocco, Jr., D.O, a board-certified dermatologist at OhioHealth Physician Group in Marion, Ohio, adds that the PASI doesn’t provide a complete picture of a person’s condition. “It does not consider daily life activities, such as work, being a parent, having personal relationships, or sleep disturbance,” Morocco says. “It also does not rate symptoms, such as itching and pain.”

Your doctor will likely use a combination of scores and physical examinations to determine the severity of your psoriasis and make recommendations for treatment based on a more complete picture, Morocco says. “We are treating more than a disease—we are treating the whole person,” he says. “Psoriasis is a complicated disease and, unfortunately, there may never be one simplified measuring tool that can assess the complexity of this chronic condition.”

Still, if you’re interested in how you rate on the PASI scale, here’s what you should know.

What Does the PASI Measure?

Psoriasis, a chronic immune-mediated disease, can cause thick, long-lasting skin lesions called plaques to appear on your skin. These plaques can itch and scale and may cause some pain. The PASI is used to measure the redness, scaling, and thickness of psoriasis plaques, as well as how much of the body is covered with them.

What Is a PASI Score?

PASI scores range from 0 (no psoriasis) to 72. The higher the score, the greater the psoriasis severity, Morocco says. Scoring is broken down as follows:

  • 0 to 5 is considered mild
  • 5 to 10 is considered moderate
  • 10 or more is considered severe

Dermatologists use these scores to help guide treatment recommendations. For example, topical medication may be appropriate for mild psoriasis, whereas systemic medicine may be necessary to treat moderate to severe cases, Morocco says.

How to Calculate a PASI Score

To calculate a PASI score, the body is divided into four regions:

  • head
  • arms
  • trunk
  • legs

In each area, the redness, thickness, and scaliness of psoriasis lesions are graded on a scale of 0 to 4—0 meaning no involvement and 4 meaning severe involvement. Each area is calculated and then totaled.

The final score is higher when redness, thickness, and scaliness are more pronounced.

Can You Score Yourself?

You can find a number of online tools, such as this PASI score calculator, to help you score your psoriasis severity on your own.

“They are safe in that there is no biopsy or scraping needed to perform the test,” Morocco says. However, he says, online calculators are based on features that are hard to discern unless you’re a trained professional. So, do-it-yourself scores can be unreliable.

Even two trained professionals may score someone’s psoriasis differently because the scoring is somewhat subjective, Morocco adds.

If you’re using online calculators, Yamauchi recommends experimenting with more than one to compare results and hopefully get closer to an accurate score.

What Are the Advantages to PASI?

The PASI is helpful for clinical trials, Yamauchi says, because the data can be compared quickly. “Dermatologists are accustomed to seeing PASI scores when looking at data,” he says. “It gives a valid numerical score at baseline that can be recalculated after treatment to either show improvement or if the treatment plan is not successful,” Morocco adds.

What Are the Disadvantages to PASI?

Besides providing an incomplete picture and being complicated to calculate, PASI scores are also not as reliable for people with mild psoriasis. “When scores are less than 3, they are not as precise,” Yamauchi says.

That’s why most physicians determine psoriasis severity using a combination of three different factors, Morocco says:

  • The percentage of body surface area covered by psoriasis
  • An estimate of plaque severity based on physical exam findings
  • The impact that psoriasis has on the person

Are There Alternative Scoring Systems?

One alternative to the PASI is the Physician Global Assessment (PGA), Yamauchi says. Another is the Body Surface Area of Involvement (BSA).

PGA is a six-point scale (0 to 5) of rating the psoriasis as clear, almost clear, mild, moderate, or severe. The scoring is based on redness, scaling, and thickness of psoriasis plaques. A dermatologist performs a physical exam to assign a numerical score, Yamauchi says.

The BSA is the total percentage of skin affected by psoriasis. The palm of a person’s hand is about 1% of their BSA.

A BSA total less than 3% is mild; moderate is 3% to 10%; and severe is more than 10%.

Another determining factor to consider is the location of the psoriasis, Yamauchi says. “If the psoriasis occurs on challenging areas of the body, like the scalp, palms or soles, genitalia, or nails, even if the BSA is less than 10%, it can be rated as severe based on the PGA,” he says.

What the Scores Mean to You

The more accurate your score, the easier for you and your doctor to determine how to best treat your psoriasis. But your score isn’t the only factor that should be considered. Your overall treatment strategy should be based on a variety of factors:

  • The severity of your psoriasis
  • How it affects your quality of life
  • Your treatment preferences
  • Your personal goals for treatment

There really is no need for you to keep track of your PASI, PGA, or BSA on your own—unless you want to. Most people can tell if their psoriasis is improving because they notice they have less psoriasis than before. But if you enjoy looking at data, you can try scoring along the way.

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