NRD_visitLink is one of two data elements created specifically for the Nationwide Readmissions Database (NRD) for tracking patients across hospitals in a year. The timing information in NRD_DaysToEvent must be used in tandem with the visit linkage variable (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 person identified by NRD_visitLink cannot be cannot be followed across data years.

The patient's date of birth and sex were used to qualify the encrypted patient linkage numbers provided to HCUP. A new verified patient linkage number (NRD_visitLink) was assigned for each unique combination of the qualifying information (encrypted patient linkage number, date of birth, and sex). Consider the following example: Five records have the same encrypted patient linkage number, 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 patient linkage number is assigned if any of the three pieces of information was missing (i.e., NRD_visitLink is missing). Additionally, no verified patient linkage number is assigned if there were more than 40 hospital visits in a given calendar year with the same qualifying information. This second qualification excluded less than 0.5 percent of the patient linkage numbers.

While the term "verified patient linkage number" is used to describe the data element NRD_visitLink, the values are not recognizable as specific patient information. VisitLink does not include the values of the encrypted patient linkage number, date of birth, or sex.