The invention presents a method of diagnosing or monitoring the status of systemic lupus erythematosus (SLE) in a subject or patient comprising detecting the expression of all genes of a diagnostic set in the subject or patient wherein the diagnostic set comprises two or more genes having expression correlated with the classification or status of SLE; and diagnosing or monitoring the status of SLE in the subject or patient by applying at least one statistical method to the expression of the genes of the diagnostic set.