tell me the name of the last lab test that patient 31482 got since 04/2105?
select d_labitems.label from d_labitems where d_labitems.itemid in ( select labevents.itemid from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 31482 ) and strftime('%y-%m',labevents.charttime) >= '2105-04' order by labevents.charttime desc limit 1 )