When adding the 'Patient ID' within the QRDA1 'patientRole' section, we use patient's 'MRN' as part of the value included as @extension. Is there a specific format or restrictions for the 'Patient ID'? Could a combination of 'MRN+system person_id' be used as 'Patient ID' in the QRDA to ensure the uniqueness of the identifier? We have seen hospital systems where the same MRN is used for different patients (maybe they have created MRN for different settings, ex. lab, acute, outpatient, etc). Combining the MRN with the system patient_id meets the goal of having a unique patient identifier. Your guidance will be appreciated.