The verified encrypted patient linkage number (VisitLink) is one of two data elements created specifically for the HCUP State Databases for tracking hospital encounters for individual patients across hospitals and hospital settings while adhering to strict privacy regulations. The timing information in DaysToEvent must be used in tandem with VisitLink. Before using the revisit variables, please refer to HCUP Supplemental Variables for Revisit Analyses for information on how they are constructed and change over time.

Please note that the values of VisitLink are unique within a state, but not across states. For example, a unique value of VisitLink will track a patient within a state, such as the 2020 California SID, SASD, and SEDD, but the same value of VisitLink may be also be used for a different patient in another state, such as 2020 New York SID, SASD, and SEDD. In addition, Partners sometimes change their coding scheme between data years, which in turn causes a discontinuity in VisitLink.

The value is assigned based on a unique combination of the de-identified patient number provided by the HCUP Partner, date of birth and sex. Consider the following example: five records have the same de-identified patient number provided by the HCUP Partner, but two records have one date of birth and sex, and the remaining three records have a different, but consistent, date of birth and sex. The two records with identical identifying information have one value of VisitLink, and the other three records have a different value of VisitLink.

No verified encrypted patient linkage number is assigned if any of the three pieces of information is missing (i.e., VisitLink is missing). Additionally, no verified encrypted patient linkage number is assigned if there are more than 40 hospital visits in a given calendar year with the same qualifying information. This second qualification sets less than 0.5 percent of the verified encrypted patient linkage numbers to missing.

While the term "verified encrypted patient linkage number" is used to describe the data element VisitLink, the values are not recognizable as specific patient information. VisitLink does not include the values of the de-identified patient number provided by the HCUP Partner or the patient's date of birth or sex.

Beginning with the 2009 HCUP data, the revisit variables (VisitLink and DaysToEvent) are included in the Core file of the SID, SASD, and SEDD files, when possible. For 2003-2008 data, the revisit variables are in separate HCUP Supplemental Files for Revisit Analyses.