UB04 Field 3b: Medical Record Number

Introduction

Field 3b (also known as Box 3b) on the UB-04 claim form is used to record the patient's unique Medical Record Number (MRN) assigned by the provider's accounting or health information management system. While this field serves as a critical internal identifier for tracking patient history and reconciling accounts, it is generally considered optional for the adjudication of the claim itself.

Requirements

Requirement Type	Status
Inpatient Requirement	Not Required
Outpatient Requirement	Not Required
Field Name	Medical Record Number
Location	Box 3b

Billing Tips

Although Box 3b is not required for claim processing and will not be reflected on the Explanation of Benefits (EOB), it is highly recommended to include the Medical Record Number to facilitate easier internal auditing and payment posting. Ensure the number entered matches your internal records to streamline communication between the billing department and clinical staff.