what is patient 1902's minimum value of absolute cd3 count since 1 month ago?
select min(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 1902 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'absolute cd3 count' ) and datetime(labevents.charttime) >= datetime(current_time,'-1 month')