instruction: what was the name of the specimen test that patient 031-4423 had first received on their last hospital encounter?
response: SELECT microlab.culturesite FROM microlab WHERE microlab.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '031-4423' AND NOT patient.hospitaldischargetime IS NULL ORDER BY patient.hospitaladmittime DESC LIMIT 1)) ORDER BY microlab.culturetakentime LIMIT 1