###HUMAN: so what's the average mch value of patient 006-157753 on their current hospital encounter?, ###ASSISTANT: SELECT AVG(lab.labresult) FROM lab WHERE lab.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '006-157753' AND patient.hospitaldischargetime IS NULL)) AND lab.labname = 'mch'