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NIS Description of Data Elements
The NIS is set of longitudinal hospital inpatient databases included in the HCUP family. These databases are created by AHRQ through a Federal-State-Industry partnership.
PRSYS - Procedure coding system
Documentation Sections:
General Notes
Uniform Values
State Specific Notes
General Notes

PRSYS indicates the coding system for the procedures:

  • Almost all HCUP inpatient stays use ICD-9-CM procedure codes (PRSYS = 1)
  • If Physicians' Current Procedural Terminology (CPT) or HCFA Common Procedure Coding System (HCPCS) procedure codes are indicated (PRSYS = 2 or 3), then the procedure codes 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 (PRn) are 4 characters in length.
  • If the procedure coding system was not specified by the data source, then PRSYS is missing (PRSYS =l .)

The data element PRSYS was discontinued in 1998.

Uniform Values
VariableDescriptionValueValue Description
PRSYSProcedure coding system1ICD-9-CM
State Specific Notes


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

  • Prior to 1995, Pennsylvania supplied only ICD-9-CM procedure codes (PRSYS = 1).
  • From 1995-1996, Pennsylvania supplied a mixture of ICD-9-CM, CPT and HCPCS codes. PRSYS which identifies the procedure coding system was assigned based on the value reported by the data source (PRSYS = 1, 2, or 3).
  • In 1997, Pennsylvania source documentation indicated that all procedure codes were ICD-9-CM codes (PRSYS = 1).. Any procedure codes that were suspected of being CPT or HCPCS codes were masked during HCUP processing.
  • Beginning in 1998, Pennsylvania supplied only ICD-9-CM procedure codes.

See the Pennsylvania note on procedures (PRn) for more specific details.


Prior to 1995, CPT and HCPCS procedure codes were not included in the Pennsylvania data.

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.

In 1997, CPT and HCPCS procedure codes do not occur in the data supplied by Pennsylvania.


Internet Citation: HCUP NIS Description of Data Elements. Healthcare Cost and Utilization Project (HCUP). September 2008. Agency for Healthcare Research and Quality, Rockville, MD.
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Last modified 9/17/08