instruction: how much has patient 84346's urea nitrogen changed or differed last measured on the last hospital visit compared to the value first measured on the last hospital visit?
response: SELECT (SELECT labevents.valuenum FROM labevents WHERE labevents.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 84346 AND NOT admissions.dischtime IS NULL ORDER BY admissions.admittime DESC LIMIT 1) AND labevents.itemid IN (SELECT d_labitems.itemid FROM d_labitems WHERE d_labitems.label = 'urea nitrogen') ORDER BY labevents.charttime DESC LIMIT 1) - (SELECT labevents.valuenum FROM labevents WHERE labevents.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 84346 AND NOT admissions.dischtime IS NULL ORDER BY admissions.admittime DESC LIMIT 1) AND labevents.itemid IN (SELECT d_labitems.itemid FROM d_labitems WHERE d_labitems.label = 'urea nitrogen') ORDER BY labevents.charttime LIMIT 1)