when had patient 72107 received the sodium lab test for the last time when they came to the hospital first time?
select labevents.charttime from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'sodium' ) and labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 72107 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) order by labevents.charttime desc limit 1