UB04 Field 66: Diagnosis/Procedure Code Qualifier

Overview

Field 66 on the UB-04 claim form, titled “Diagnosis/Procedure Code Qualifier” (also referred to as the ICD Version Indicator), is a required data element for all institutional claims, both inpatient and outpatient. ^[1] lists this field under its UB-04 instructions, and both ^[2] and ^[3] explicitly state “FL 66 – Diagnosis and Procedure code Qualifier (ICD Version Indicator) Required.” The purpose of this qualifier is to denote which version of the International Classification of Diseases (ICD) is being reported on the claim. ^[2] specifies two valid qualifier codes: “9” for the Ninth Revision (ICD-9) and “0” for the Tenth Revision (ICD-10). The field ensures that the payer correctly interprets the diagnosis and procedure codes submitted in other fields, especially given that ICD-9 and ICD-10 codes have different structures and lengths. Proper completion of Field 66 is a prerequisite for accurate claim processing and payment.

When to Use

Field 66 must be completed on every UB-04 claim that includes any diagnosis or procedure code. ^[1] includes it as a mandatory field in its instruction set, and both ^[2] and ^[3] confirm that the field is required. The qualifier is used for all claims, regardless of provider type (e.g., acute care hospitals, long-term care, outpatient clinics) and regardless of payer (Medicare, Medicaid, commercial insurance). Because the field indicates the ICD version in use, it is particularly critical during transition periods (e.g., after the ICD-10 implementation in October 2015) or when a claim includes codes from only one revision. Even if the claim uses only ICD-10 codes, the qualifier “0” must be entered. If a provider inadvertently leaves Field 66 blank, the claim will likely be rejected or pended for manual review. The qualifier must match the version of the codes reported in Field 67 (Principal Diagnosis), Field 69 (Admitting Diagnosis), Field 70 (Patient’s Reason for Visit), and Field 72 (External Cause of Injury), as well as procedure codes in Field 74 (Principal Procedure and Other Procedures). ^[1] lists these related fields in its table of contents, underscoring their interdependence.

Step-by-Step Claim Example

Consider a hypothetical hospital claim submitted in 2024 where all diagnosis codes are from ICD-10. The billing specialist completes Field 66 by entering the qualifier “0” (Tenth Revision). This is based on the instruction in ^[2] that “0” denotes the Tenth Revision. Step 1: Verify that every diagnosis code on the claim – Principal Diagnosis (Field 67), Admitting Diagnosis (Field 69), and any Other Diagnosis codes (Fields 67A–67Q) – is an ICD-10 code (e.g., I21.4 for NSTEMI). Step 2: Confirm that all procedure codes in Field 74 are also ICD-10-PCS codes (e.g., 02H63JZ for insertion of drug-eluting stent). Step 3: Enter “0” in the two‑digit subfield of Box 66 (the qualifier is typically entered as a single digit, but the field on the UB-04 allows for a one‑ or two‑digit indicator; CMS instructions use a single digit). Step 4: Cross‑check that no ICD-9 codes are present on the claim. If the claim were for a historical period when ICD-9 was still in use, the qualifier “9” would be entered instead. ^[1] lists Field 66 in its UB-04 flow, indicating it is processed alongside diagnosis fields. Once completed, the qualifier tells the payer’s system to read the codes using the ICD-10 code set, ensuring correct grouping and reimbursement. The example shows that Field 66 is a simple but essential field; a single character can affect the entire claim’s adjudication.

Common Mistakes & Audit Red Flags

Several errors in Field 66 can trigger claim denials or audit flags. The most common mistake is leaving the field blank. Because ^[3] states the field is “Required,” a blank will cause the claim to be rejected. Another frequent error is using an outdated qualifier, such as entering “9” when the claim contains ICD-10 codes, or vice versa. ^[2] explicitly defines only “9” and “0,” so any other value (e.g., “1” or “A”) is invalid and will be rejected. A third mistake is inconsistency between the qualifier and the actual codes on the claim. For instance, entering “9” but then submitting an ICD‑10 diagnosis code (e.g., J44.9) in Field 67 will cause the payer’s system to mismatch, often resulting in a claim suspension or denial. Auditors specifically look for such mismatches because they indicate possible coding errors or fraud. ^[1] includes Field 66 in its UB-04 instructions, and payers will compare the qualifier with the diagnosis and procedure fields. Additionally, if a claim contains a mix of ICD‑9 and ICD‑10 codes (e.g., due to a crossover from older records), Field 66 cannot handle two versions – it must match the version used for the primary codes. Providers should ensure that all codes on the claim belong to the same revision. Finally, some billing systems may default to an old qualifier; regular audits of exported claims should verify Field 66. To avoid red flags, always complete Field 66 and confirm it aligns with the code set used throughout the claim.

Related Codes/Fields

Field 66’s value directly impacts how the following fields are interpreted. The table below lists the most relevant related fields on the UB-04, all of which are referenced in ^[1]’s table of contents.

Field Number	Field Name	Relationship to Field 66
67	Principal Diagnosis Code	The qualifier in Field 66 determines the ICD version used to read this code.
67A–67Q	Other Diagnosis Codes	Same qualifier applies to all additional diagnoses; must match version.
69	Admitting Diagnosis Code	Must be consistent with the qualifier in Field 66.
70A–70C	Patient’s Reason for Visit/Chief Complaint	ICD version qualifier ensures correct interpretation of these visit reason codes.
72A–72C	External Cause of Injury Code (E‑Code)	The qualifier indicates whether E‑codes are ICD‑9 (E‑codes) or ICD‑10 (external cause codes).
74	Principal Procedure Code	Procedure codes (ICD‑9‑CM or ICD‑10‑PCS) must match the version specified in Field 66.
74A–74E	Other Procedure Codes	All procedure codes must use the same version denoted by the qualifier.

The qualifier in Field 66 is essential for the accurate processing of every diagnosis and procedure code on the claim, as confirmed by ^[2] and ^[1]. Without the correct qualifier, payers cannot reliably interpret the clinical data that drives reimbursement.

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References

[1] Maryland Medicaid FL 66 — https://health.maryland.gov/mmcp/provider/Documents/ffs-billing/UB04-Hospital-Billing-Instructions%20%281%29.pdf

[2] CMS Chapter 25 — https://www.cms.gov/regulations-and-guidance/guidance/manuals/downloads/clm104c25.pdf

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