how many days have elapsed since the last time in their current hospital visit patient 42829 has been given a white blood cells lab test?
select 1 * ( strftime('%j',current_time) - strftime('%j',labevents.charttime) ) from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'white blood cells' ) and labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 42829 and admissions.dischtime is null ) order by labevents.charttime desc limit 1