Detection of factor H autoantibodies. Factor H autoantibodies in aHUS patients and control subjects were detected by the use of a sensitive ELISA as described in “Factor H autoantibody assay.” (A) OD492 for 100 control subjects and 142 aHUS patients. (B) OD492 for 8 control subjects and 37 aHUS patients with an uncorrected OD value greater than or close to 0.215 (the mean + 2SD for the 100 control subjects) after background reactivity to BSA has been subtracted to exclude false-positive interactions. The identity of the 13 factor H autoantibody–positive patients is shown.