instruction: what number of hours have passed since patient 55281 last received a potassium lab test during their current hospital encounter?
response: SELECT 24 * (STRFTIME('%j', CURRENT_TIME()) - STRFTIME('%j', labevents.charttime)) FROM labevents WHERE labevents.itemid IN (SELECT d_labitems.itemid FROM d_labitems WHERE d_labitems.label = 'potassium') AND labevents.hadm_id IN (SELECT admissions.hadm_id FROM admissions WHERE admissions.subject_id = 55281 AND admissions.dischtime IS NULL) ORDER BY labevents.charttime DESC LIMIT 1