UB04 Field 3b: Medical Record Number

Overview

Field 3b (Medical Record Number) on the UB-04 claim form is a situational data element used to capture the patient’s medical or health record number as assigned by the provider. Unlike Field 3a (which holds the patient’s Health Insurance Claim Number, typically the Medicare ID), Field 3b is reserved for the provider’s internal tracking identifier for the patient’s medical record. This field is not required for either inpatient or outpatient claims, but its presence can support internal record matching and continuity of care documentation. The CMS instructions specify that the number assigned to the patient’s medical/health record by the provider should be entered here, not the number from Field 3a. ^[1] and ^[2]

When to Use

Field 3b is situational and may be completed when the provider maintains a distinct medical record numbering system separate from the patient’s health insurance claim number. It is particularly relevant in settings where the provider’s internal record ID differs from the Medicare ID or other payer identifiers. For example, a hospital may assign a unique medical record number (MRN) to each patient upon admission, which is used for internal tracking, indexing, and retrieval of clinical information. This MRN should be entered in Field 3b when the UB-04 is submitted for billing purposes. The field is not mandatory, so it may be left blank if the provider does not use a separate numbering system or if the MRN is already captured elsewhere in the claim. However, when completed, it must accurately reflect the provider-assigned record number, not the patient’s HICN or other external identifiers. ^[1] and ^[2]

Step-by-Step Claim Example

To illustrate proper completion of Field 3b, consider a patient admitted to a hospital with a Medicare HICN of 12345-678A. The hospital assigns this patient a medical record number of MRN-987654. On the UB-04 claim form:

• Field 3a (Health Insurance Claim Number) would be populated with “12345-678A” as the Medicare identifier.
• Field 3b (Medical Record Number) would be populated with “MRN-987654” as the provider’s internal record number.

The claim should also include the patient’s name, date of birth, and other required demographic and billing data. The MRN in Field 3b must match the number used in the provider’s internal systems; it is not interchangeable with the HICN. If the provider does not use a distinct MRN, Field 3b may be omitted. However, if the MRN is present, it must be accurate and consistent with the provider’s records. ^[2] and ^[1]

Common Mistakes & Audit Red Flags

Auditors and claim reviewers may identify discrepancies when Field 3b contains a number that does not match the provider’s internal medical record system or when the field is used to report a payer identifier instead of the provider-assigned record number. Common mistakes include:

• Entering the patient’s Health Insurance Claim Number (HICN) in Field 3b instead of the provider’s MRN.
• Leaving Field 3b blank when the provider does maintain a separate MRN, potentially causing internal record linkage issues.
• Using a non-standard format or including extraneous characters (e.g., dashes, spaces) that do not align with the provider’s record numbering convention.
• Populating Field 3b with a number that is inconsistent with the medical record number documented elsewhere in the patient’s chart or billing system.

To avoid audit flags, ensure that Field 3b is completed only with the provider-assigned medical record number, and that this number matches the internal records. If the provider does not use a separate MRN, the field should be left blank. Consistency between Field 3b and the provider’s documentation is critical for accurate claim processing and record reconciliation. ^[2] and ^[1]

Related Codes/Fields (markdown table)

Field	Description	Usage Context
FL 3a	Health Insurance Claim Number (HICN)	Required for Medicare claims; identifies the patient’s insurance identifier.
FL 3b	Medical/Health Record Number	Situational; provider-assigned internal record number for the patient.
FL 4	Type of Bill	Required; four-digit alphanumeric code specifying bill type, leading zero ignored by CMS.
FL 5	Federal Tax Number	Required for certain provider types; identifies the billing entity’s tax ID.
FL 6	Statement Covers Period	Required; dates of service covered by the claim.
FL 7	Covered Days	Required for inpatient claims; number of days covered by the bill.
FL 8	Noncovered Days	Situational; days not covered by Medicare or other payer.
FL 9	Coinsurance Days	Situational; days subject to coinsurance for inpatient claims.
FL 10	Condition Code	Situational; codes indicating special conditions or circumstances affecting the claim.
FL 11	Occurrence Code	Situational; codes for specific events or occurrences relevant to the claim.
FL 12	Occurrence Span Code	Situational; codes for time spans of occurrences.
FL 13	Occurrence Span From/Through	Situational; dates for occurrence spans.

| FL 14 | Occur

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References

[1] Source: CMS Chapter 25, FL 3b — https://www.cms.gov/regulations-and-guidance/guidance/manuals/downloads/clm104c25.pdf

[2] CMS R1915CP — https://www.cms.gov/Regulations-and-Guidance/Guidance/Transmittals/downloads/R1915CP.pdf