instruction: provide the number of patients diagnosed under the icd9 code 5849 whose lab test category is hematology.
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 = "5849" AND lab."CATEGORY" = "Hematology"