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Central Distributor SID: Description of Data Elements

ZIP_S - Synthetic patient zip code
Documentation Sections:
General Notes
Uniform Values
State Specific Notes
General Notes

ZIP_S contains a fixed-key (one-to-one) encryption of the patient's residential zip code (ZIP). To prevent inadvertent or intentional identification of specific patients based on the patient's residential zip code, the last 2 digits were encrypted. While it is still possible to identify the state of a patient's residence using the first three unencrypted zip code digits, ZIP_S does not allow placement of a specific patient within a narrower, zip code-based geography.

If the zip code in the HCUP outpatient surgery databases and the inpatient databases are the same, the synthetic identifier, ZIP_S is the same.

Users of the encrypted zip code data element are strictly forbidden to identify the actual zip code associated with the encrypted zip code.

The encrypted zip code (ZIP_S) contains the following special values:

  • Canadian, Mexican, and other or unspecified foreign zip codes (ZIP_S = "C", "M", or "F", respectively).
  • Invalid zip codes (ZIP = "A"). In the 1988-1992 HCUP databases, the zip code is validated against a composite list of zip codes valid as of December 1987, 1990, and 1992. Beginning in the 1993 HCUP databases, the zip code is required only to be numeric.
  • Homeless patients. In the 1988-1999 HCUP databases, (ZIP_S = " ") . Beginning in the 2000 HCUP databases, ZIP_S = "H".
Uniform Values
VariableDescriptionValueValue Description
ZIP_SSynthetic patient zip codennnnnSynthetic zip codes
FOther or unspecified foreign
HHomeless (beginning with 2000 data)
BUnavailable from source (coded 1988-1997 data only)
State Specific Notes


Arkansas does not separately classify Canadian, Mexican, or other foreign zip codes.


Hawaii uses only one category for all foreign zip codes, including Canada and Mexico. These are assigned to the HCUP category for Other/Unspecified Foreign (ZIP_S = "F").


Maine does not separately classify Canadian, Mexican, or other foreign zip codes.


Internet Citation: HCUP Central Distributor SID Description of Data Elements - All States. Healthcare Cost and Utilization Project (HCUP). May 2024. Agency for Healthcare Research and Quality, Rockville, MD.
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Last modified 5/22/24