Psoriasis is usually diagnosed by a general practitioner or dermatologist. It is most often a clinical diagnosis, meaning that the physical examination findings alone make the diagnosis clear. In different people, psoriasis tends to show similar skin changes, such as redness, thick skin, scaling, itching, and pain, and appear in the same areas (elbows, knees, and scalp, among others).
When the clinical diagnosis is clear, a person will often need no laboratory tests. There are no blood tests needed to diagnose or treat psoriasis, however, blood tests may be used to monitor medications or to check for joint disease activity.
At times, the diagnosis of psoriasis may be unclear. This uncertainty may arise because skin changes appear in unexpected areas, look unusual, or are infected. When the diagnosis is not obvious, a physician will often need to sample the skin with a skin biopsy, a procedure that is usually performed by a dermatologist.
After diagnosis, a patient may be referred to a dermatologist for continuing care and treatment adjustments. A dermatologist’s input is especially important if psoriasis is severe, hard to treat, changes unexpectedly, or causes a great deal of distress to the patient.