what was the last time patient 4718 had a peripheral blood lymphocytes microbiology test in the last hospital visit?
select microbiologyevents.charttime from microbiologyevents where microbiologyevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 4718 and admissions.dischtime is not null order by admissions.admittime desc limit 1 ) and microbiologyevents.spec_type_desc = 'peripheral blood lymphocytes' order by microbiologyevents.charttime desc limit 1