what is the change/difference in hematocrit of patient 93078 measured at 2105-12-31 21:06:00 compared to the value measured at 2105-12-31 15:11:00?
select ( select labevents.valuenum from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 93078 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'hematocrit' ) and labevents.charttime = '2105-12-31 21:06:00' ) - ( select labevents.valuenum from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 93078 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'hematocrit' ) and labevents.charttime = '2105-12-31 15:11:00' )