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.