oh what is the average value of creatinine on patient 64881 since 53 months ago?
select avg(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 64881 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'creatinine' ) and datetime(labevents.charttime) >= datetime(current_time,'-53 month')