what is the average macrophages value until 08/2104 for patient 1798?
select avg(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 1798 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'macrophages' ) and strftime('%y-%m',labevents.charttime) <= '2104-08'