calculate the number of patients who had received a bilirubin, total, ascites test since 6 years 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 = 'bilirubin, total, ascites' ) and datetime(labevents.charttime) >= datetime(current_time,'-6 year') )