hey what was the last ptt of patient 63849 since 11/2103?
select labevents.valuenum from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 63849 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'ptt' ) and strftime('%y-%m',labevents.charttime) >= '2103-11' order by labevents.charttime desc limit 1