what was the last value of a lab test of anion gap since 168 months ago for patient 65786?
select labevents.valuenum from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 65786 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'anion gap' ) and datetime(labevents.charttime) >= datetime(current_time,'-168 month') order by labevents.charttime desc limit 1