what's patient 74392's minimum value of bilirubin, direct?
select min(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 74392 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'bilirubin, direct' )