Date of procedure performed (PRDATEn) is assigned a valid nonmissing date, with the following exceptions:

• If a procedure date is supplied by the data source, but one or more of the components of the procedure date (year, month, day) is
  • Blank or a documented missing value, PRDATEn = missing (.).
  • - or -
  • Nonnumeric or out of range (year NE 00-99, month NE 1-12, day NE 1-31), PRDATEn = invalid (.A).
• PRDATEn = invalid (.A) if the procedure day is inconsistent with the month (e.g., February 30).
• If the data source does not supply procedure date, then beginning in the 1998 data, PRDATEn is not present on the HCUP files. In the 1988-1997 data, PRDATEn is retained on the HCUP files and is set to unavailable from source (.B).
• PRDATEn is inconsistent (.C) if
  • there is a day of procedure without a coded procedure (ED7nn), or
  • the day of procedure is not during the stay (EPRDAY01 beginning in the 1998 data and ED8nn in the 1988-1997 data).
• Edit checks ED7nn are only performed on the 1988-1997 data. Beginning in the 1998 data, the procedure date without a coded procedure is discarded.

The procedure date vector (PRDATEn) is shifted with the ICD-9-CM procedure codes (PRn) when the procedure vector is packed.

Some sources do not require procedure dates for minor or diagnostic procedures which are considered UHDDS class 3 and class 4 procedures. The UHDDS system grouped ICD-9-CM procedure codes into four classes differentiated by impact on either the well-being of the patient or on the health care system. The criteria used to classify procedures included procedural risk, anesthetic risk, and the need for highly trained personnel, special facilities or special equipment. The classes are:

• Class 1: Surgical
• Class 2: Significant procedure (date required)
• Class 3: Significant procedure (date not required)
• Class 4: Minor procedures not normally coded on inpatient data.

To ensure the confidentiality of patients on the HCUP Central Distributor files, full dates are not released. Beginning in the 1998 data, PRDATEn is replaced by procedure month (PRMONTHn) and procedure year (PRYEARn). In databases before 1998, the day portion of the date stored in PRDATEn is overwritten with "01" during the creation of the Distributor files. The month and year portion of the date remains unchanged. HCUP data elements that are calculated from PRDATEn are computed before PRDATEn is masked.