instruction: during the current hospital visit how many times did patient 016-9636 get a ptt test?
response: SELECT COUNT(*) FROM lab WHERE lab.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '016-9636' AND patient.hospitaldischargetime IS NULL)) AND lab.labname = 'ptt'