instruction: how many days is it since patient 002-34744's first mch lab test during their current hospital visit?
response: SELECT 1 * (STRFTIME('%j', CURRENT_TIME()) - STRFTIME('%j', lab.labresulttime)) FROM lab WHERE lab.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '002-34744' AND patient.hospitaldischargetime IS NULL)) AND lab.labname = 'mch' ORDER BY lab.labresulttime LIMIT 1