In data prior to the fourth quarter of 2015, International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) procedures reported on HCUP records are stored in the data elements PRn. Beginning in the fourth quarter of 2015, International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) procedures reported on HCUP records are stored in the data elements I10_DXn.

In the HCUP databases, ICD-9-CM procedures are represented as 3- to 4-character numeric codes with implicit decimals (i.e., decimals not included). Prior to data year 2014, the HCUP data elements for ICD-9-CM procedures are length 4; in 2014, they are length 7. The codes are left-justified in the HCUP databases so that prior to 2014 there is one space following a 3-digit procedure code (four spaces, in 2014). For example, the procedure code 37.0 would appear as '370 ' with a trailing blank in HCUP data. Any zeroes at the beginning of the code are significant; they are part of the code. Any zeroes at the beginning of the code are significant; they are part of the code. For example, the ICD-9-CM procedure code 03.1 would be stored in the HCUP databases as '031 ' and the diagnosis 003.1 would be stored as '0031'.

The original value of the ICD-9-CM first-listed procedure (PR1), whether blank or coded, is retained in the first position of the procedure vector. Starting at the first secondary procedure (PR2), the procedures are shifted during HCUP processing to eliminate blank secondary procedures. For example, if PR2 and PR4 contain nonmissing procedures and PR3 is blank, then the value of PR4 is shifted into PR3. Secondary procedures are never shifted into the first listed position (PR1).

Procedures are compared to a list of ICD-9-CM codes valid for the discharge date. Anticipation of or lags in response to official ICD-9-CM coding changes are permitted for discharges occurring within a window of time around the official ICD-9-CM coding changes (usually October 1). Prior to 1998 data, a six months window (three months before and three months after) is allowed. Beginning in the 1998 data, a year window (six months before and six months after) is allowed. If the procedure contains intermittent blank characters or is zero filled, then the procedure will be considered invalid.

Procedures are compared to the sex of the patient (edit check EPR03 beginning in the 1998 data and ED2nn prior to 1998 data) and the patient's age (edit check EAGE05 beginning in the 1998 data and ED5nn prior to 1998 data) for checking the internal consistency of the record.

How invalid and inconsistent codes are handled varies by data year.

• Beginning in the 1998 data, invalid and inconsistent procedures are masked directly. Validity flags are not included on the HCUP record. Clinical Classifications Software (CCS) data elements are coded with respect to the procedure.

• Prior to 1998 data, invalid and inconsistent procedures are retained on the record. Validity flags (PRVn) indicate invalid, inconsistent procedure codes. Clinical Classifications Software (CCS) data elements use the former name (PCCHPRn). The CCS was formerly known as the Clinical Classifications for Health Policy Research (CCHPRn). The procedure related data element are coded as follows:

The validity flags (PRVn) need to be used in connection with any analysis of the procedures (PRn).

The maximum number of procedures reported varies by state. HCUP retains all procedure fields provided by the data source.

Since NPR can be greater than the number of procedures available on the inpatient record, caution needs to be taken when using NPR to loop through the procedures. A counter for the loop should not extend past 15. Programming code such as the following example SAS statement is needed to take this into account:

DO I = 1 to MIN (15, NPR); Followed by code to process all procedures. END;

Beginning in 1998, a few hospitals reported 5-digit codes in the procedure fields. Since ICD-9-CM procedures are have either 3 or 4 digits, these five digit codes were set to invalid.

Beginning in 1993, Arizona procedure codes were not right-padded with zeros. Arizona reported procedure codes with an explicit decimal point. The decimal point was removed during HCUP processing.

Prior to 1993, the procedure codes provided by Arizona were right-padded with zeros (e.g., the procedure code '403 ' was supplied as '4030'). The following algorithm was used during HCUP processing to validate the procedure codes:

Check four-digit code for validity (using a six-month window for coding changes, 3 months before and 3 months after October of each year when ICD-9-CM coding changes occur).

1. If four-digit code is valid, set PR1 to the four-digit code and set PRV1 = 0.
2. If the four-digit code is invalid and fourth digit is a zero, create a three-digit code by deleting the trailing zero and re-check for validity (using six-month window for coding changes). If the three-digit code is valid, set PR1 to the three-digit code and set PRV1 = 0.
3. If both the four-digit and three-digit codes are invalid, save the original four-digit code PR1 and set the validity flag to indicate an invalid code (PRV1 = 1).

Shriner's hospitals do not report diagnoses, procedures or total charges.

In 1992 only, the hospitals identified below have erroneous procedure information when a patient had more than one operative episode during a stay. The first operative episode, which can be defined by one or more procedure codes, is correctly reported. The procedure codes for any subsequent operative episodes were not reported. The following hospitals, identified by the HCUP hospital identifier (HOSPID), are affected:

• 390530
• 390170
• 391000
• 390067
• 390622
• 390870
• 390060
• 391060
• 390727
• 390515
• 390034

Kentucky supplied procedure codes in a field length of 7. Only the first four characters contained in the left-justified source field were used to assign the HCUP procedure codes.

Maryland supplied procedure codes in a field of length 5. Only the first four characters contained in the left-justified source field were used to assign the HCUP procedure codes.

Due to an error in HCUP processing, the procedure verification table for 1988-1992 incorrectly accepted some codes as valid, on year beyond the date when these codes were deleted or superseded by more detailed codes. With the three-month grace period built into the processor, these codes were mistakenly accepted for one full year beyond the year in which they became invalid.

Examination of frequencies from the HCUP Massachusetts files found a small number of records were affected. The procedures not flagged as invalid procedure codes (PRVn = 1) are:

Beginning in 1993, procedures were validated correctly.

CPT-4 and ICD-9-CM procedure codes were mixed together in the source supplied array of procedures. The CPT-4 procedures were moved into the HCUP array for CPT-4 codes (CPTn) and the ICD-9-CM procedures were packed into the HCUP array for ICD-9-CM codes (PRn). The first listed procedure was retained in the first position and all subsequent procedures were packed so there are no empty spots after the second position of the array (i.e., CPT2 or PR2).

Nebraska supplied procedure codes in a field of length 7. Only the first four characters contained in the left-justified source field were used to assign the HCUP procedure codes.

Nevada supplied procedure codes in a field of length 10. Only the first four characters contained in the left-justified source field were used to assign the HCUP procedure codes.

Before 1994, the procedure codes provided by the state were right-padded with zeros (e.g., the procedure code '403' was supplied as '4030'). For the HCUP database the following algorithm was used to validate the procedure codes:

Check the four-digit code for validity (using a six-month window for coding changes, 3 months before and 3 months after October of each year when ICD-9-CM coding changes occur).

1. If the four-digit code is valid, set PRn to the four-digit code and set PRVn = 0.
2. If the four-digit code is invalid and the fourth digit is a zero**, create a three-digit code by deleting the trailing zero and re-check for validity (using six-month window for coding changes). If valid, set PRn to the three-digit code and set PRVn = 0.
3. If both the four-digit and the three-digit codes are invalid, save the original four-digit code PRn and set the validity flag to indicate an invalid code (PRVn = 1).

In 1993 only. Due to an error in HCUP processing, the invalid three-digit code was saved in PRn instead of the invalid four-digit code.

** In 1993 only. An error in HCUP processing caused invalid four-digit codes that ended in non-zeros, as well as zeros, to be processed by the above algorithm. If deleting the rightmost non-zero digit created a valid code, then

• PRn was set to the stripped valid code,
• PRVn was set 0 to indicate a valid code,
• PCCHPR was set based on the stripped valid code, and
• DRG, MDC, DRG10, MDC10, NEOMAT and edit check variables ED100, ED2nn, and ED5nn may have been incorrectly assigned based on the stripped valid code.

Beginning in 2008, New York suppressed the identifier for the hospital (DSHOSPID) on records with an indication of induced abortion. These records are retained in the HCUP SID with the DSHOSPID set to "BLNK". New York identifies an indication of induced abortion by ICD-9-CM diagnosis or procedure code:

• An admitting, principal, or secondary diagnosis of "6350" through "6399", or "7796".
• A principal or secondary procedure of "690", "695", "696", "6993", "738", "7491", "750", or "9649".

Ohio supplied procedure codes in a field of length 9. Only the first four characters contained in the left-justified source field were used to assign the HCUP procedure codes.

The reporting and handling of CPT and HCPCS procedure codes varies by year:

• Prior to 1995, Pennsylvania supplied only ICD-9-CM procedure codes.
• From 1995-1996, Pennsylvania supplied a mixture of ICD-9-CM, CPT and HCPCS codes. If the procedure coding system indicates CPT or HCPCS codes on the record, then the codes are set to missing. Details are provided below.
• In 1997, Pennsylvania source documentation indicated that all procedure codes were ICD-9-CM codes. Any procedure codes that were suspected of being CPT or HCPCS codes were masked during HCUP processing. Details are provided below.
• Beginning in 1998, Pennsylvania supplied only ICD-9-CM procedure codes.

Handling CPT and HCPCS Codes in 1995-1996

In 1995-1996, Pennsylvania reports ICD-9-CM procedure codes on most of their discharges, but some use CPT and HCPCS procedure codes.

HCUP processed the Pennsylvania procedure codes as follows.

1. PRSYS which identifies the procedure coding system was assigned based on the value reported by the data source.
2. NPR is the number of non-missing procedure codes supplied by Pennsylvania, regardless of coding system.
3. How HCUP processing handles the procedure codes depends on the coding system.
• ICD-9-CM procedure codes (PRSYS = 1) are retained as supplied by the data source in the PRn variables and validated. Results from the validation are indicated by the PRVn variables. No changes are made to the procedure codes.
• CPT or HCPCS procedure codes (PRSYS = 2 or 3) are set to missing (PRn = blank). CPT and HCPCS procedure codes could not be retained in the HCUP data because they are 5 characters, and the HCUP procedure fields are 4 characters in length.
• If the procedure coding system was invalid (PRSYS = .A) or missing (PRSYS = .), then the procedures are handled like ICD-9-CM procedure codes. Any non-missing procedure codes are retained in the PRn variables and validated. Results from the validation are indicated by the PRVn variables. Source documentation indicates that missing values for PRSYS are only allowed when no procedures are coded.

Warning: If a CPT or HCPCS procedure code was reported on a discharge in which the procedure coding system was missing, or invalid, or indicated as ICD-9-CM, then only the first four characters of the five-digit code would be retained in the PRn variable.

Handling Suspected CPT and HCPCS Codes in 1997

Even though the Pennsylvania source documentation reported that all procedures in 1997 were coded in ICD-9-CM, there were a small percentage of codes that looked suspiciously like CPT or HCPCS codes which are length 5 and start with an alphabetic character. ICD-9-CM procedure codes have no more than 4 digits and do not contain alphabetic characters (A-Z). To ensure that no CPT and HCPCS procedure codes were included in the 1997 Pennsylvania data, procedure codes were "screened" during HCUP processing.

If a procedure code was longer than 4 digits or started with an alphabetic character (A-Z), then the procedure was suspected of being a CPT or HCPCS procedure code and handled as follows:

• the procedure (PRn) was set to "PPPP",
• the validity flag (PRVn) was set to 1, and
• the classification system (PCCHPRn) was set to invalid (.A).

Otherwise, the procedure code was validated against a list of ICD-9-CM procedure codes with respect to discharge date.

From 1995-1996, the number of discharges for which the procedure coding system indicated that the procedures were CPT or HCPCS (PRSYS = 2 or 3) follows:

• NIS, Release 4 (1995 data) has no records.
• NIS, Release 5 (1996 data) has 1,711 records.

Rhode Island supplied procedure codes in a field of length 5. Only the first four characters contained in the left-justified source field were used to assign the HCUP procedure codes.

In the 2004 outpatient data from South Carolina, there were a number of records with X-filled values in the list of procedures. This data source attempted to translate any CPT procedure codes into ICD-9-CM procedure codes. If this was not possible, the data source masked the CPT code with X's. During HCUP data processing, the X-filled values were discarded, and the procedure array was packed to eliminate the blank entries.

Also in 2004, we suspect that some South Carolina hospitals truncated their CPT codes to four digits instead of masking them with X's. The following hospitals have a large number of invalid ICD-9-CM procedure codes: DSHOSPID 045, 090, 1405, 370, 420, 565, 670. The invalid ICD-9-CM procedure codes look suspiciously like truncated CPT codes. It is also possible that some of the truncated CPT procedure codes were not identified because the 4-digit value was a valid ICD-9-CM code.

Prior to 2000 data, a small number of discharges explicitly included decimals in the procedure field, usually the decimal is implicit. This is problematic because South Carolina supplied procedures in a field of length 4. If decimals were included, then a valid 4-digit code would be truncated. For example, the procedure for a simple mastoidectomy "2041" would be incorrectly reported as "20.4". Prior to 1998, invalid procedure codes are marked by a validity flag (PRVn = 1). Beginning in 1998, invalid procedure codes are masked (PRn = "invl"). Beginning in 2000 data this was no longer a problem; explicit decimals were not included in the procedure codes.

South Dakota supplied procedure codes in a field of length 9. Only the first four characters contained in the left-justified source field were used to assign the HCUP procedure codes.

Texas provides the procedure codes as reported by the hospital. Source documentation indicates that these procedure codes may be a mixture of ICD-9-CM, CPT or HCPCS codes. Because CPT and HCPCS codes are length 5 and the HCUP procedure variables (PRn) are length 4, the last digit of the CPT and HCPCS code is excluded.

Vermont supplied procedure codes in a field length of 7. Only the first four characters contained in the left-justified source field were used to assign the HCUP procedure codes.

Washington supplied procedure codes in a field of length 5. Only the first four characters of five contained the procedure code and were used to assign the HCUP procedure code.

West Virginia supplied procedure codes in a field length of 7. Only the first four characters contained in the left-justified source field were used to assign the HCUP procedure codes.

To comply with statutory requirements, Wisconsin modified diagnosis and procedure codes that explicitly referenced induced termination of pregnancy to eliminate distinctions between induced and spontaneous termination. The following codes were modified:

• Diagnoses with the first three digit of 634, 635, 636, 637, 638 were recoded to 637, while retaining the reported fourth digit,
• Procedure 6901 was changed to 6902,
• Procedure 6951 was changed to 6952,
• Procedure 6993 was changed to 6999,
• Procedure 7491 was changed to 7499,
• Procedure 750 was changed to 7599, and
• Procedures 9641-9649 were changed to 964 (which would be flagged as invalid, PRV=1).

Beginning Q4 2015, the following codes were modified:

• Diagnosis Z33.2 was changed to Z31.9,
• Diagnoses O04x and O07x were changed to O03.9,
• Procedure 10A07ZZ was changed to 10D17ZZ,
• Procedure 10A08ZZ was changed to 10D18ZZ,
• Procedure 10A07ZZ was changed to 10D17ZZ,
• Procedure 10A08ZZ was changed to 10D18ZZ,
• Procedure 10A07ZW was changed to 0UCB7ZZ,
• Procedure 10A00ZZ was changed to 10D00Z0,
• Procedure 10A03ZZ was changed to 0UC93ZZ,
• Procedure 10A04ZZ was changed to 0UC94ZZ,
• Procedure 10A07ZX was changed to 3E0P7GC.

Wisconsin supplied ICD-9-CM procedure codes in a field length of 5. Only the first four characters contained in the left-justified source field were used to assign the HCUP procedure codes.

CPT codes submitted in the emergency department and ambulatory surgery files were converted to ICD-9-CM procedure codes by the Wisconsin Hospital Association using the current Thomson Reuters Procedure Conversion Files. When a CPT code does not convert to an ICD-9-CM code, four 'X' (XXXX) characters were placed in the ICD field. These X-filled codes are recoded as missing prior to HCUP processing to prevent them being set to invalid.

For 2013, several facilities unintentionally duplicated the principal procedure in the secondary procedure fields on some records.

Beginning Q4 2015, the Wisconsin Hospital Association will no longer convert CPT procedure codes to ICD procedure codes.