how much of a difference has patient 1561 made in its white blood cells levels last measured on the current hospital visit compared to the second to last value measured on the current hospital visit?
select ( select labevents.valuenum from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 1561 and admissions.dischtime is null ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'white blood cells' ) order by labevents.charttime desc limit 1 ) - ( select labevents.valuenum from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 1561 and admissions.dischtime is null ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'white blood cells' ) order by labevents.charttime desc limit 1 offset 1 )