what is the number of patients that received a amylase, body fluid test?
select count( distinct admissions.subject_id ) from admissions where admissions.hadm_id in ( select labevents.hadm_id from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'amylase, body fluid' ) )