instruction: what is patient 18678's monthly maximum mchc level in 2104?
response: SELECT MAX(labevents.valuenum) FROM labevents WHERE labevents.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 18678) AND labevents.itemid IN (SELECT d_labitems.itemid FROM d_labitems WHERE d_labitems.label = 'mchc') AND STRFTIME('%y', labevents.charttime) = '2104' GROUP BY STRFTIME('%y-%m', labevents.charttime)