instruction: Give me the number of patients whose drug code was morp2-4 and had lab test category as hematology.
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN prescriptions ON demographic.hadm_id = prescriptions.hadm_id INNER JOIN lab ON demographic.hadm_id = lab.hadm_id WHERE prescriptions.formulary_drug_cd = "MORP2-4" AND lab."CATEGORY" = "Hematology"