instruction: how many patients are diagnosed with icd9 code 44020 and tested under category hematology in lab?
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id INNER JOIN lab ON demographic.hadm_id = lab.hadm_id WHERE diagnoses.icd9_code = "44020" AND lab."CATEGORY" = "Hematology"