Usually, your doctor will make a diagnosis of psoriasis based on the appearance of your skin. There is no blood test for psoriasis.
In rare cases, a small sample of skin, called a biopsy, will be sent to the laboratory for examination under a microscope. This will determine the exact type of psoriasis and will rule out other skin disorders, such as seborrhoeic dermatitis, lichen planus, lichen simplex and pityriasis rosea.
If your doctor suspects you have psoriatic arthritis, which is sometimes a complication of psoriasis, you may be referred to a rheumatologist, who specialises in arthritis. You may have blood tests to rule out other conditions, and X-rays of the affected joints may be taken.
