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Central Distributor SEDD: Description of Data Elements

MRN_R - Medical record number (re-identified)
Documentation Sections:
General Notes
Uniform Values
State Specific Notes
General Notes

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

Because of a change in the algorithm for creating person identifiers, patients cannot be tracked from before 2003 to after 2003. In HCUP data prior to 2003, a synthetic medical record number (MRN_S), created using fixed-key encryption, was available. Starting in data year 2003, a reidentification number (MRN_R) was used. MRN_R includes an arbitrarily chosen, identifying number that is unique to the medical record identifier provided to HCUP.

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

    Frequencies of the number of discharges per nonmissing MRN_R, by hospital, and

    Hospital-level counts of the number of unique nonmissing MRN_Rs, the number of discharges associated with these MRN_Rs, the ratio of these two numbers (discharges/person), and the number of discharges without a MRN_R.

Uniform Values
VariableDescriptionValueValue Description
MRN_RMedical record number (re-identified)9(n)Medical record number
State Specific Notes


Beginning with 2019, Arizona uses a different masking method. The coding of Medical Record Number is not consistent with prior years.


The Hawaii medical record number (MRN_R) cannot be used to track patients consistently over time from 2003 to 2004. Hawaii provides a re-identification medical record number. Hawaii reported that there were problems with the consistent assignment of the re-identified MRNs in 2004. Beginning with 2005, the patient should retain the same re-identification number across years, which permits readmission studies from 2005 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.


Caution should be used when using MRN_S to track patients back to 1999. The values supplied by the data source in the 1999 data appear different from the values supplied beginning in 2000.

Maine provides encrypted medical record numbers. During HCUP processing, medical record numbers were re-encrypted (MRN_R).


Beginning in 2007, Maryland included the records from all other outpatients, Greenbaum cancer center, and UMMS shock trauma in the unified AS and ED outpatient data file. The inclusion of these new records resulted in a large increase in Re-identified Medical Record Number.

Beginning in 2006, Medical Record Numbers were encrypted during the HCUP processing.

Maryland supplied an encrypted Medical Record Number. During HCUP processing, this encrypted identifier was assigned to MRN and re-encrypted for MRN_R.

In the 2001 SASD, the coding of the source provided medical record number appears inconsistent with other years. Prior to 2001, the supplied values have eleven (11) characters. In 2001, the supplied values have four to nine (4-9) characters. The inpatient and emergency department data provided to HCUP by Maryland include an eleven character medical record number in all years.


Beginning in Q4 of 2015 the source values changed. Therefore, MRN_R is not consistent with data from prior years.

New Jersey

In 2018 the source values changed; therefore, they are not consistent with data from 2014-2017.

In 2014 the source values changed; therefore, they are not consistent with data from previous years.

Prior to the 2010 data year, mothers' medical record numbers were encrypted using a specific encryption routine that is different from the routine used to encrypt medical record numbers. Because of the use of different encryption routines for these two fields, values in the MOMNUM_R field do not match the values in MRN_R field.


Beginning in 2015 the source values changed. Therefore, MRN_R is not consistent with data from prior years.


Beginning in 2008 the source values changed; therefore, they are not consistent with data from previous years.

Again in 2010, the source values changed and they are not consistent with previous years.


Internet Citation: HCUP Central Distributor SEDD Description of Data Elements - All States. Healthcare Cost and Utilization Project (HCUP). September 2008. Agency for Healthcare Research and Quality, Rockville, MD.
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Last modified 9/11/08