Diagnosis
A diagnosis of psoriasis is usually based on the appearance of the skin; there are no special blood tests or diagnostic procedures. Sometimes, a skin biopsy, or scraping, may be needed to rule out other disorders and to confirm the diagnosis. Skin from a biopsy will show clubbed rete pegs if positive for psoriasis. Another sign of psoriasis is that when the plaques are scraped, one can see pinpoint bleeding from the skin below (Auspitz's sign).
Read more about this topic: Psoriasis