How Is Psoriasis Diagnosed?

Medically reviewed by Brendan Camp, MD

A physical exam and skin biopsy can test for and diagnose psoriasis. Psoriasis is an autoimmune disorder that speeds up the growth of skin cells and causes raised, thick patches on the body. These patches are called "plaques" and can be itchy and painful. More than 7.5 million people over the age of 20 in the United States have psoriasis.

This number may be higher since psoriasis can be difficult to diagnose. Psoriasis can look like other skin conditions, such as eczema. Symptoms are also often underdiagnosed in people with darker skin tones.

It's a good idea to see a healthcare provider if you think you have symptoms or are at risk of psoriasis. A dermatologist (a healthcare provider who specializes in the skin) will typically ask you about your medical history and perform a physical exam to examine any plaques, rashes, or scales on your skin. They may also sometimes order a skin biopsy to reach a more accurate diagnosis.

Related: How Are Allergies Diagnosed?

Medical History

A healthcare provider will usually ask about your medical history, lifestyle, and any changes or stressors. Some questions may include:

• Does anyone in your family have psoriasis?

• Have you experienced any significant life changes or stressors recently?

• What symptoms do you have? How long have you had symptoms?

A healthcare provider might also ask if you're experiencing joint pain, swelling, or stiffness. This may sound like a strange question, but some evidence suggests that as many as 42% of people with psoriasis also develop psoriatic arthritis (PsA). PsA causes inflammation in the skin and the joints.

Physical Exam

A healthcare provider or dermatologist will look at any plaques, scales, or rashes on your body. Many dermatologists can diagnose psoriasis by looking at your skin, nails, or scalp. They may also use a dermatoscope. This tool has a light and zooms in on your skin to help examine and identify your plaques.

Not all plaques look the same. People with darker skin tones can have purple or brown plaques, accompanied by gray scales. People with lighter skin tones may have pink or red plaques with white scales.

Psoriasis is more common in White people and those of European descent. The skin condition is also underdiagnosed in people with darker skin tones. Researchers have typically conducted studies on those with lighter skin. It can be difficult for people with darker skin to get an accurate diagnosis, so more research is needed.

A dermatologist will generally know what to look for in different skin tones. The National Psoriasis Foundation has developed a Skin of Color Resource Center, which can provide additional resources on how to receive a second opinion and a proper diagnosis.

Skin Biopsy

Psoriatic plaques can resemble other skin conditions, such as eczema and contact dermatitis. To diagnose psoriasis properly, a healthcare provider may also order a skin biopsy. This procedure uses a device to take a small sample of your skin. The provider will send the sample to a lab to be tested.

The main ways to perform a biopsy include:

• Punch biopsy: If plaques are formed in deeper skin layers, a healthcare provider will use a round blade to take a skin sample.

• Shave biopsy: This procedure uses a razor blade to remove a sample of your skin. A shave biopsy is typically only done if you have small plaques on the top skin layers.

A healthcare provider will likely clean the area where they remove the skin sample before performing the biopsy. They will then give you a form of anesthesia to numb the pain.

Most skin biopsies for psoriasis are harmless. Some people may experience slight bruising, bleeding, or soreness in the affected area. These side effects usually don't last for more than a few days.

Screening for Related Conditions

A healthcare provider may use additional methods, such as patch testing and imaging tests, to rule out or test for other health conditions, like PsA.

Patch Testing

Plaques and scales are symptoms of a variety of skin concerns. Patch testing is not needed to diagnose psoriasis, but a healthcare provider may use it to determine if you have other skin conditions.

Dermatologists often use patch testing to examine the cause of rashes, itchiness, and potential allergic reactions. A patch test can take up to one week to complete over the course of a few appointments.

A healthcare provider will place several different allergens on your back and then tape those allergens with a patch. These patches must be left on your skin for 48–72 hours. The purpose of these patches is to see if your skin reacts to any of the allergens.

A healthcare provider will then remove the patches to make a note if any of the allergens give you a skin reaction. They will be able to tell you whether you have an allergy, eczema, or other skin condition if your skin has a reaction.

How Does Patch Testing Work?

A healthcare provider may apply common allergens, such as latex, hair dye, medications, pollen, and metals, to patches and then place the patches on your body. Patch testing does not require needles.

Imaging Tests

Imaging tests, like X-rays and MRIs, are not used to diagnose psoriasis. You may be at risk of PsA if you receive a psoriasis diagnosis. Nearly one-third of people with psoriasis also have PsA. This is known as a co-morbid, or co-occurring, condition.

What is Psoriatic Arthritis (PsA)?

PsA is a chronic inflammatory disease that causes joint pain, stiffness, and swelling. The disease most commonly occurs in people ages 30–50 but can affect anyone, including children.

A healthcare provider will likely use imaging tests to examine your joint tissue more closely. Imaging tests create detailed images of your joints, which can help a healthcare provider look for any changes or damage to your tissue or bones. They will generally order imaging tests for your hands, knees, and feet. In the early stages of PsA, the smaller joints in your body are generally affected.

A healthcare provider will consult with a rheumatologist (a healthcare provider who specializes in the joints and muscles) if they notice damage or concerns with your joint tissue. They will refer you to a dermatologist to help create a treatment plan right for you.

Related: How Is Scabies Diagnosed?

A Quick Review

Psoriasis is a skin condition that causes raised, thick skin patches. A healthcare provider will not use one test to diagnose this disease. Instead, they will use a variety of tests, including a medical history, physical exam, and skin biopsy. You may need patch testing or imaging tests to potentially detect other skin conditions associated with psoriasis.

Psoriasis symptoms can be painful and uncomfortable. You may find it beneficial to visit a healthcare provider for an exam if you notice skin changes. Receiving an early diagnosis can help you better manage symptoms and prevent further irritation or discomfort to your skin. 

FAQs

Frequently Asked Questions

1. Can a blood test detect psoriasis?

There are no blood tests available to detect psoriasis. A healthcare provider can typically diagnose the skin condition with a medical history and physical exam. They may sometimes use a skin biopsy for a more accurate diagnosis.

2. Can psoriasis cause a positive ANA test?

An antinuclear antibody (ANA) test helps diagnose autoimmune disorders. A positive ANA test may signal that your immune system is overactive, meaning it's targeting and attacking healthy tissues.

Psoriasis is an autoimmune disorder, so you might have a positive ANA test. A positive test cannot confirm a psoriasis diagnosis.

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