The day on which the procedure is performed (PRDAYn) is calculated from the procedure date (PRDATEn) and the admission date (ADATE) with the following exceptions:

• PRDAYn is set to the supplied day of principal procedure if the procedure day cannot be calculated (ADATE and/or PRDATEn is missing or invalid). Note: the supplied day of procedure is used only if it distinguishes between a procedure performed on the first day (procedure day = 0) and no procedure day (procedure day is missing).
• PRDAYn is missing (.) if the procedure day cannot be calculated and the supplied procedure day is missing.
• PRDAYn is invalid (.A) if the procedure day cannot be calculated and the supplied procedure day is nonnumeric.
• If the data source does not supply either admission date (ADATE) and procedure date (PRDATEn), or the day of procedure, then beginning in the 1998 data PRDAYn is not present on the HCUP files. In the 1988-1997 data, PRDAYn is retained on the HCUP files and is set to unavailable from source (.B).
• PRDAYn 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/days 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.

PRDAY1 is present on the NIS from 1988 onward; secondary procedures (PRDAY2-15) are present on the NIS beginning in 1998.

Prior to 2008, only PRDAY1 is available because Arizona did not report secondary procedure days or dates. Beginning in 2008, Arizona provides dates for all secondary procedures.

Beginning in 1995, only the calculated day of procedure could be used to assign PRDAY because Arizona did not supply the day of procedure. Prior to 1995, no procedure dates or days were reported.

Prior to 1998, the supplied day of procedure was not used when PRDAY could not be calculated because California used the same value to indicate no procedure performed and procedure performed on the day of admission.

In 1998 and 1999, only the supplied day of procedure could be used to assign PRDAY because the date of procedure was not provided. A source value of 0 days was set to missing (PRDAYn = .) if there was no corresponding procedure (PRn = " ").

Beginning in 2000, procedure dates were provided by the data source and used to calculate day of procedure.

Beginning in 2010, Colorado began supplying secondary procedure dates. These fields are used to calculate PRDAYn.

Prior to 2010, only PRDAY1 is available because Colorado did not report secondary procedure days or dates.

Only the calculated day of principal procedure could be used to assign PRDAY1 because Colorado did not supply principal procedure day.

Procedures performed up to 72 hours before admission are reported as zero (0) days.

If the procedure was performed on the admission date, then PRDAYn equals 0.

Beginning with 2006, Florida provided procedure days for the principal and all secondary procedures.

For 2004 - 2005, only PRDAY1 is available because Florida did not report secondary procedure days or dates.

Through 2003, PRDAY1 is assigned from the supplied day of procedure. Florida did not supply the procedure date for these years. A missing value (.) was assigned from either of the following values supplied by the data source: 998 an indicator that the number of days to procedure is greater than or equal to 998 days; and 999 an indicator of unable-to-compute days, or that no procedure was performed.

Florida also used zeros to code both missing values and a procedure performed on the day of admission. During HCUP processing, PRDAY1 was set to missing (.) if

• the reported procedure day = 0, and
• no principal procedure was reported.

Only the calculated day of procedure could be used to assign PRDAYn because Hawaii did not supply the day of procedure.

Beginning with 2009, Illinois resumed providing procedure days for the principal and all secondary procedures.

For 1998 to 2008, no procedure days or dates were reported.

For 1988 to 1997, Illinois provided procedure days for the principal and all secondary procedures.

Prior to 2010, only PRDAY1 is available because Indiana did not report secondary procedure days or dates. Beginning in 2010, Indiana started supplying secondary procedure dates.

Only the calculated day of procedure could be used to assign PRDAYn because Indiana did not supply this information.

Only the calculated day of procedure could be used to assign PRDAY because Iowa did not supply the day of procedure.

Beginning with 2005, Kansas provided procedure dates, which were used to calculate day of procedure.

Prior to 2005, no procedure days or dates were reported.

Only the calculated day of procedure could be used to assign PRDAYn because Maine did not supply procedure days.

Beginning in 2013, the HCUP Maryland SID includes 30 procedure days. Previously, the HCUP Maryland SID included 11 procedure days (PRDAYn).

Beginning with October 2006, PRDAY4-15 were calculated during the HCUP data processing.

Beginning with October 2006, Massachusetts provided procedure dates for all procedure fields.

From 2003 through Sept 2006, Massachusetts supplied three procedure date fields.

Prior to 2003, the supplied day of procedure was not used when PRDAYn could not be calculated because Massachusetts used the same value to indicate no procedure performed and procedure performed on the day of admission.

Prior to 2007, only PRDAY1 is available because Michigan did not report secondary procedure days or dates.

Only the calculated day of procedure could be used to assign PRDAYn because Minnesota did not supply day of procedure.

Only the calculated day of procedure could be used to assign PRDAYn because Nebraska did not supply day of procedure.

Beginning in 2008, Nevada supplied secondary procedure dates.

Prior to 2008, only PRDAY1 is available.

Only the calculated day of procedure could be used to assign PRDAY because New Jersey did not supply the day of procedure.

In the 1988-1997 HCUP New York databases, PRDAYn could not be calculated because New York did not report full admission and procedure dates. During HCUP processing, only the reported procedure day could be used to assign PRDAYn. For 1988-1992, the source miscalculated procedure days for records with admission dates in the year prior to discharge, resulting in procedure days that were not during the stay. These records failed the appropriate edit check. Beginning in 1993, the source correctly calculated procedure days for all procedures.

Beginning with the 2008 data, the HCUP data element PRDAYn is missing (.) for AIDS/HIV patients. New York identifies AIDS/HIV records by ICD-9-CM diagnosis code, DRG, or MS-DRG:

• An admitting, principal or any secondary diagnosis of "042", "043", "044", "7958", "27910", "27919", "2793", "1363", "79571", "07951", "07952", "07953", "V017" or "V08".
• A DRG of 488 through 490 (prior to October 2007) or MS-DRG of 700 through 716 (beginning in October 2007).

Please note that the admitting diagnosis is not retained in the HCUP databases prior to 2012.

Only the reported day of procedure could be used to assign PRDAYn because North Carolina did not supply procedure dates.

Only the calculated day of procedure could be used to assign PRDAYn because North Dakota did not supply day of procedure.

Only the calculated day of procedure could be used to assign PRDAYn because Oregon did not supply procedure days.

In 1992, Pennsylvania data contained many out-of-range procedure days due to a processing error at the state data organization. As a rule in HCUP processing, records that contain procedure days not during the stay are flagged by an edit check and the procedure day (PRDAYn) is set to inconsistent (.C).

In 1994, principal procedure days could not be calculated for all patients admitted prior to January 1, 1994 because the source did not report a valid principal procedure date for these patients. Procedure days were calculated correctly for secondary procedures.

In 1995, the data source arbitrarily set the year of procedure date equal to the discharge year. This results in a number of out-of-range procedure days. Records that contain procedure days not during the stay are flagged by an edit check and the procedure data and day are set to inconsistent (.C).

Also in 1995, a data processing error in the source data resulted in a number of records with procedure dates without matching procedures. These records are flagged by an edit check during HCUP processing.

By 1996, all major problems with procedure dates were resolved.

Only the calculated day of procedure could be used to assign PRDAYn because Rhode Island did not supply day of procedure.

Only the calculated day of procedure could be used to assign PRDAYn because South Carolina did not supply the day of procedure.

Only the calculated day of procedure could be used to assign PRDAYn because South Dakota did not supply day of procedure.

Only the calculated day of procedure could be used to assign PRDAYn because Tennessee did not supply the day of procedure.

Beginning in 2010, Virginia provided the numbers of days from admission that are associated with secondary procedures.

Only PRDAY1 is available because Virginia did not report secondary procedure days or dates.

Only the supplied day of procedure could be used to assign PRDAY because the date of procedure was not provided.

Beginning with 1998, only PRDAY1 is available because Wisconsin did not report secondary procedure days or dates.

Until 1997, PRDAYn could not be calculated because Wisconsin did not report procedure dates. During HCUP processing, only the reported procedure day could be used to assign PRDAYn. Beginning in 1997, Wisconsin provided the date of principal procedure (PRDATE1).

Principal procedure day is only required for major procedures (defined below). Procedure days are set to missing for all other cases.

Major procedures are defined as Class 1 or 2 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