tell me the first lab test that was given to patient 18517 on their last hospital encounter?
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 = 18517 and admissions.dischtime is not null order by admissions.admittime desc limit 1 ) order by labevents.charttime asc limit 1 )