Did she mean that his blood work was negative for Lupus? But, the biopsy was positive for Discoid Lupus? I am not a doctor so I cannot say why the dermatologist did not do a medical history or if she can make a diagnosis of discoid lupus with just a blood test. However, doing a biopsy on the skin can often tell if lesions are caused by Lupus.
The symptoms of Discoid Lupus can include: aching muscles, aching joints, chronic fatigue, positive skin biopsy for discoid, butterfly rash, rash on feet (disc-like), reaction to the sun, anemia. If you have a positive ANA with discoid lupus, this will heighten the concern for the possibility of Systemic Lupus Erythematosus (SLE). If you are unclear about or not confident about your diagnosis, you should discuss this with your doctor. If you have a rheumatologist, his opinion can clarify the diagnosis of discoid and/or systemic lupus.
Peace and Blessings