ขอทราบจำนวนผู้ป่วยที่ได้รับการวินิจฉัยภายใต้รหัส icd9 76528 และประเภทการทดสอบในห้องปฏิบัติการคือเคมี ไม่จำเป็นต้องใช้ตารางทั้งหมด
give me the number of patients who were diagnosed under icd9 code 76528 and also their lab test category is chemistry.It is not neccessary to use all the tables.
 demographic:  subject_id [ text]  hadm_id [ text]  name [ text]  marital_status [ text]  age [ text]  dob [ text]  gender [ text]  language [ text]  religion [ text]  admission_type [ text]  days_stay [ text]  insurance [ text]  ethnicity [ text]  expire_flag [ text]  admission_location [ text]  discharge_location [ text]  diagnosis [ text]  dod [ text]  dob_year [ text]  dod_year [ text]  admittime [ text]  dischtime [ text]  admityear [ text] 
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 = "76528" AND lab."CATEGORY" = "Chemistry"