instruction: calculate the number of times until 3 years ago patient 19691 has received a mcv lab test.
response: SELECT COUNT(*) FROM labevents WHERE labevents.itemid IN (SELECT d_labitems.itemid FROM d_labitems WHERE d_labitems.label = 'mcv') AND labevents.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 19691) AND DATETIME(labevents.charttime) <= DATETIME(CURRENT_TIME(), '-3 year')