instruction: are there any results of the microbiological test for patient 17638's blood (cmv ab) since 4 years ago?
response: 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')