How is sle diagnosed?  

History physical lab. It takes an involved evaluation. We do it with a complex consultation looking at history, physical, laboratory evaluation + imaging. It takes a lot of work. Of interest the government stopped paying for consultations with medicare patients. It has deemed that it is too confusing to use it but we as rheumatologists need it to evaluate complex rheumatology patients like those with lupus. Go figure.
See answer. With a careful history, physical examination and lab testing by a clinician experienced with systemic lupus erythematosus, often over the course of time. There are diagnostic criteria to guide the decision making process but these are not hard and fast rules.