The Procedure Classes categorizes ICD-9-CM procedure codes into one of four broad categories:

• Minor Diagnostic: Non-operating room procedures that are diagnostic (e.g., 87.03 CT scan of head)
• Minor Therapeutic - Non-operating room procedures that are therapeutic (e.g., 02.41 Irrigate ventricular shunt)
• Major Diagnostic - All procedures considered valid operating room procedures by the Diagnosis Related Group (DRG) grouper and that are performed for diagnostic reasons (e.g., 01.14 Open brain biopsy)
• Major Therapeutic - All procedures considered valid operating room procedures by the Diagnosis Related Group (DRG) grouper and that are performed for therapeutic reasons (e.g., 39.24 Aorta-renal bypass).

PCLASS_IPn is coded as follows:

• 1 to 4 if the procedure code (PR_IPn) is valid by the HCUP criteria. PCLASS_IPn is missing (.), if there is no procedure code (PR_IPn = " ").
• PCLASS_IPn is set to invalid (.A), if the procedure code (PR_IPn) is invalid by the HCUP criteria.
• PCLASS_IPn is set to inconsistent (.C), if the procedure code (PR_IPn) is inconsistent with age or sex of the patient.