A patient record is based on the patient's master patient index (MPI) number and medical record number (MRN). The MPI and MRN uniquely identify the patient in the medical system.
A patient can have only one MPI, but that MPI can be associated with multiple MRNs. Typically, each MPI and MRN must be unique. However, you can configure OnBase to support non-unique (overlapping) MRNs and MPIs, but additional steps are required. See Overlapping Identifiers and Assigning Authorities.