The data element NRD_VisitLink is one of two data elements created specifically for the Nationwide Readmissions Database (NRD) for tracking inpatient stays for individual patients across hospitals in a year. The timing information in NRD_DaysToEvent must be used in tandem with the verified encrypted patient linkage number (NRD_VisitLink). These variables enable users to study multiple hospital visits for the same patient across hospitals and time while adhering to strict privacy regulations.

NRD_VisitLink does not link to other HCUP databases or to external databases. In addition, the values of NRD_VisitLink differ from year to year. An individual patient identified by NRD_VisitLink cannot be followed across data years.

NRD_VisitLink is the data element that links all inpatient stays associated with a unique patient. All discharges in the NRD include a value for NRD_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 NRD_VisitLink, and the other three records have a different value of NRD_VisitLink.

No verified encrypted patient linkage number is assigned if any of the three pieces of information is missing (i.e., NRD_VisitLink is missing). Additionally, no verified encrypted patient linkage number is assigned if there are more than 40 inpatient stays in a given calendar year with the same qualifying information. This second qualification excludes less than 0.5 percent of records in a data year.

While the term "verified encrypted patient linkage number" is used to describe the data element NRD_VisitLink, the values are not recognizable as specific patient information. NRD_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.