Skip Navigation
MRN_S - Synthetic medical record number
Documentation Sections:
General Notes
Uniform Values
State Specific Notes
General Notes

Beginning in 2003, this data element is called MRN_R.

MRN_S is specific to patients (persons) so that multiple admissions by the same patient to a single institution can be linked. MRN_S does not allow linkage of persons across institutions.

MRN_S should not be used for analyses without first consulting summary statistics on:

  • Frequencies of the number of discharges per nonmissing MRN_S, by hospital, and
  • Hospital-level counts of the number of unique nonmissing MRN_Ss, the number of discharges associated with these MRN_Ss, the ratio of these two numbers (discharges/person), and the number of discharges without a MRN_S.

MRN_S contains a fixed-key (one-to-one) encryption of the supplied medical record number (MRN), according to the following rules:

  • All alphanumeric digits are used in the encryption.
  • All symbols such as ".,:;'*@" are retained in the encrypted value but not in the same location.
  • Leading zeros are retained. If a hospital codes the same medical record number inconsistently (sometimes with leading zeros and sometimes with leading blanks), the HCUP medical record numbers are different.
  • When the MRN in the ambulatory surgery data and the inpatient data are the same, the synthetic identifier, MRN_S is the same.

Beginning in the 1993 data, the medical record numbers were checked for null characters. If null characters were found, they were replaced by blanks before the number was encrypted. Since this conversion was not done in prior years of HCUP data, the encrypted medical record numbers from 1993 on may not match those in earlier years. However, null characters are rarely included.

Uniform Values
VariableDescriptionValueValue Description
MRN_SSynthetic medical record number17(a)Synthetic medical record number
State Specific Notes


The Hawaii medical record number (MRN_S) cannot be used to track patients consistently over time because the coding scheme changed in 2002 and again in 2003. Beginning in 2002, Hawaii assigns a re-identification number to the reported medical record numbers. The re-identification number is not based on any systematically applied set of rules. In addition, Hawaii reports that patients were assigned new re-identification numbers each year in 2002 and 2003. This does not allow for readmission studies across years or longitudinal analysis across 2001- 2003. Beginning with 2003, the patient will retain the same re-identification number across years, which permits readmission studies from 2003 forward,

Prior to 2002, Hawaii encrypted their medical record numbers using an algorithm unique to the data organization. There is slight variation in the assignment of encrypted medical record number across years prior to 2002 due to differences in handling non-numeric characters each year and other variations of this sort. Nonetheless, the patient retains the same identification number up through 2001, which allows for readmission studies within years and longitudinal analysis across years through 2001.


Internet Citation: HCUP Central Distributor SID Description of Data Elements - All States. Healthcare Cost and Utilization Project (HCUP). August 2008. Agency for Healthcare Research and Quality, Rockville, MD.
Are you having problems viewing or printing pages on this Website?
If you have comments, suggestions, and/or questions, please contact
Privacy Notice, Viewers & Players
Last modified 8/12/08