How Is Psoriasis Diagnosed?

Psoriasis is often diagnosed by a dermatologist or primary care physician by its characteristic appearance and locations on the body. If a person has the skin changes typical of psoriasis, a diagnosis can be made clinically by examination alone. Based on the skin’s appearance due to psoriasis, a physician will usually be able to diagnose psoriasis and begin treating the skin immediately.

If psoriasis looks different than most cases, appears in an unusual location, or appears in a child, further tests may be needed. The definitive test when a  clinical diagnosis of skin disease is unclear is a skin biopsy.A biopsy refers to a small sample of skin taken for analysis under a microscope. For a biopsy, a small sample of skin (about a 0.25-inch [4-mm] core, the size of a pencil eraser) is removed for examination under the micro-scope by a dermatopathologist. A dermatopathologist is a physician who specializes in analyzing skin samples under the microscope for diagnostic clues. The findings of the dermatopathologist are summarized in a pathology report. Usually, only one test is required, but it may be repeated if the results aren’t clear or if the disease changes over time. A person can request a copy of this report for his or her records, and most physicians will find it useful to review it when planning treatment .

No blood test exists to diagnose psoriasis, and psoriasis does not cause abnormal blood tests for most people. The most common reason to draw blood when treating people for psoriasis is to make sure it is safe to begin a new medication or to watch for a medicine’s possible side effects. One exception is severe psoriasis covering much of the body, where changes in the skin’s barrier function could cause dehydration or salt imbalances.

If a person has joint pain or swelling anywhere in the body, evaluation for psoriatic arthritis is essential. This diagnosis may be made by a dermatologist, rheumatologist, orthopedist, or other joint specialist. The evaluation for psoriatic arthritis may include X-rays, joint tests, and blood panels to look for other causes of arthritis. It is important to consider a possible diagnosis of psoriatic arthritis in any person with psoriasis. To minimize the risk of permanent joint damage, prompt follow-up with appropriate tests for accurate diagnosis and treatment is important.