count the number of times patient 31880 got a macrophage lab test since 24 months ago.
select count(*) from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'macrophage' ) and labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 31880 ) and datetime(labevents.charttime) >= datetime(current_time,'-24 month')