We do not support your browser. Please take a moment and upgrade to the most recent version of Internet Explorer.
Researcher Resources


What is the University of California Research eXchange Data Explorer?


The University of California Research eXchange (UC ReX) Data Explorer enables UC investigators to identify potential research study cohorts at the five UC medical centers. Users can conduct interactive searches of data derived from patient care activities at Davis, Irvine, San Diego and San Francisco as well as UCLA.

What data is available through this tool?

Cohort counts rather than data sets are available through the UC ReX Data Explorer. These are based on de-identified data extracted from each institution’s clinical data warehouse, transformed into a common data representation, and stored in a separate, dedicated data repository at each institution. Currently, the following search terms are available for querying: Demographics, Diagnoses, Procedures, Laboratory Tests, Medications, Visit Details, Vital Signs and Vital Status.

What can UC ReX not do?

UC ReX is a cohort discovery tool, meaning only patient counts can be retrieved. Individual patient-level data cannot be accessed through this tool, but it is possible to gather this information outside of UC ReX. Please contact us directly at ucrex@mednet.ucla.edu if you would like individual patient-level data. These requests will be reviewed on a case by case basis.

Who can use the tool?

To access the UC ReX Data Explorer workbench at UCLA, researchers must be affiliated with a UCLA principal investigator and complete training.

If you would like to request access to the UC ReX Data Explorer workbench, or if you have questions, please email ucrex@mednet.ucla.edu.

Additional Resources

Training materials and background information about UC ReX is available at UC ReX Central.

Available materials include the following:


View the UC ReX Training Webinar
Please click below to view the training seminar.


How is data obtained in UC ReX?

Data is obtained from administrative records and electronic health records of patients that received care across all 5 UC medical centers.

The time range in which data is available varies by the institution and depends on the institution’s EHR database. UC ReX currently has data on 14 million unique patients and is continually being updated on a weekly or monthly basis, depending on the institution. We will display a chart with data counts across the institutions in the near future.

It is important to note that all data in UC ReX is associated with a UC-affiliated hospital, therefore, Rady Children’s Hospital will not have any data loaded into UC ReX.

There is currently no option for patients to request that his/her information be excluded from the UC ReX database, but all of the fields for every patient specified by HIPAA rules for safe harbor de-identification will be excluded from the data repository except for dates and zip codes.

More information on the source data can be found here.

Where do the ICD codes come from?

ICD codes are based on billing data from both inpatient and outpatient encounters.

What type of laboratory tests are in the UC ReX database?

UC ReX currently has the top 150 ordered laboratory tests from each UC medical school with the earliest lab data going back to 1992. Because each test has to be harmonized across the UC system, we put our focus on gathering the tests that would be most requested.

If you are interested in a specific test that is not in UC ReX, please contact us as we are interested in learning what researchers need.

What type of medications is in the UC ReX database?

We have integrated both inpatient and outpatient medications using the Anatomical Therapeutic Chemical (ATC) Classification System hierarchy.

Is each patient reported by UC ReX a unique patient?

Yes, each patient reported by UC ReX is unique to the corresponding institution. Whether a query consists of multiple ICD codes, demographics, date restrictions, etc., each patient is only counted once.

Currently, if a patient has been admitted to a different UC hospital, he/she will be viewed as a separate patient in UC ReX. This may inflate the total patient count across all institutions but we can assume that most patients are not seen at multiple UC hospitals given that each UC hospital services different regions in California.

How can I use UC ReX to recruit patients for my study?

UC ReX is a cohort discovery tool and, thus, will only provide patient counts for a specific query. To go further and receive identified patient data, you will need to follow the steps below:

  1. Obtain patient counts from all 5 UC sites using UC ReX.
  2. Recruit co-investigators at each site from which you would like to receive identified patient data.
  3. Obtain IRB approval from each institution from which you would like to receive identified patient data. If applicable, the other UC sites can use Trust and Rely to expedite their IRB approval process.
  4. Each site will then obtain the list of patients from their respective CTSI to recruit patients.

To get more information on how to access patient-level data from UC ReX, please click on the link below:

Obtaining Medical Record Data to Conduct Your Research

How does the data compare with data available through other institutions?

We performed a couple of initial comparisons between UC ReX data, data from UHC (university hospital consortium), and the state and the results reported from UC ReX were identical to the two other institutions.

Our next step in UC ReX is to perform more in-depth data quality checks. However, please report any query results that appear inaccurate so we can investigate right away.

Release Notes

Version Release: February 2016


A web browser is required to use UC ReX Data Explorer. The following four browsers are currently supported:

  • Mozilla Firefox
  • Microsoft Internet Explorer
  • Apple Safari
  • Google Chrome

Please note that JavaScript must be enabled on your web browser.

New Features:

Temporal Queries

The Temporal Query Tool extends the query functionalities provided by the classic Query Tool. Users can now define a sequence of events using time-based relationships to further add to their query criteria. For more details regarding the Temporal Query Tool, please view the following link: Temporal Query Tool

Search Concepts

New search concepts are available under the Navigate Terms pane in the Terminology Subject Areas tree. The new search concepts include:

  • Visit Details: Users can include Age at Visit, Length of Stay and Visit Type.
  • Demographics
    • Age: Users can include Age by Month for subjects under the age of 3.
    • Marital Status: Users can include Life Partner or Other.
    • Race: Users can include Multiple Races or No Information.

University of California Research eXchange (UC ReX) Data Explorer
Terms of Use

By logging in to the University of California Research eXchange (UC ReX) Data Explorer, I agree to protect the integrity and confidentiality of all information made available to me from the use of this system and to comply with the limitations on the use of this system as stated below.


  1. I agree to conduct queries only for purposes of planning research involving patients or patient data from one or more of the institutions participating in UC ReX.

  2. If I am a UC Principal Investigator, I agree to ensure that my designees with access to UC ReX agree to comply with these Terms of Use. If I am a designee of a Principal Investigator, I agree to conduct cohort discovery queries only with the full knowledge and approval of my supervising Principal Investigator.

  3. I understand that cohort discovery queries will be audited and I agree to be individually accountable for each query that is run using my account.


  1. not to share my user name or password with anyone and not to allow others to conduct queries using my account in any other way;

  2. not to attempt to identify individuals represented in the query results by any means, including use of local electronic health records or other information together with the results;

  3. not to use, disclose or distribute the results of UC ReX exploratory queries to any entity or individual for any purpose other than (1) to serve as preliminary data in research funding proposals, (2) in Institutional Review Board applications to conduct proposed research, and (3) other uses individually approved by the UC ReX Executive Committee, or as required by law;

  4. to report in writing to UC ReX program staff any use or disclosure of query results that I become aware of that are not provided for by this Agreement, including without limitation, any disclosure to an unauthorized individual or entity, within ten (10) days of its discovery;

  5. to immediately notify UC ReX program staff of any request or subpoena for query results, or other official inquiries. To the extent that the UC ReX Network institutions decide to challenge the validity of such requests, I will cooperate fully in any such challenge.