tests

Hi every one this is my first post! I am 55 years old and have had psoriasis and arthritis for about 20 years now, unfortunately covering a great deal of my body. Over the years I have visited many specialists and been given various creams, ointments etc etc but nothing has really helped. Today I visited a specialist that I have never seen before and she has told me to have various blood tests. The one thing I am very worried about is that she has also asked me to be screened for HIV and Hepatitis. As I said I have had psoriasis for 20 years and have never been asked to have this test before. There is no way I have HIV so why has she told me to have these tests? Has any one any idea? Thanks Harvey