are there any results of the microbiological test for patient 17638's blood (cmv ab) since 4 years ago?
select count(*)>0 from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 17638 ) and microbiologyevents.spec_type_desc = 'blood (cmv ab)' and datetime(microbiologyevents.charttime) >= datetime(current_time,'-4 year')