instruction: what's patient 51675's maximum value of monocytes until 40 months ago?
response: SELECT MAX(labevents.valuenum) FROM labevents WHERE labevents.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 51675) AND labevents.itemid IN (SELECT d_labitems.itemid FROM d_labitems WHERE d_labitems.label = 'monocytes') AND DATETIME(labevents.charttime) <= DATETIME(CURRENT_TIME(), '-40 month')