what are the numbers of patients who took a immunoglobulin a test since 1 year ago?
select count( distinct admissions.subject_id ) from admissions where admissions.hadm_id in ( select labevents.hadm_id from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'immunoglobulin a' ) and datetime(labevents.charttime) >= datetime(current_time,'-1 year') )