UB04 Field 11: Patient Sex

Overview

Box 11 on the UB-04 form captures the patient’s biological sex as recorded at the time of admission, outpatient service, or start of care. The field uses simple alphabetic values: M for male, F for female, and U for unknown. ^[1], while ^[2]. The requirement status differs by payer: ^[1], whereas ^[2]. Providers must consult individual payer contracts to determine whether the field is optional or mandatory. Incorrect sex coding can affect claim processing and, in some cases, clinical data analytics. The field is small but carries significant administrative and compliance implications.

When to Use

Use Box 11 whenever a UB-04 claim is submitted, but the necessity depends on the payer’s guidelines. ^[2]. ^[1]. When a payer does require it, the sex value should match the patient’s sex as documented in the medical record at the time of encounter. If the sex is unknown—a scenario ^[1]—providers should follow payer-specific rules. For payers that do not allow “U,” a missing or invalid entry may cause a claim rejection. Always verify the requirements of the specific payer before submitting the claim.

Step-by-Step Claim Example

Consider a 45-year-old female patient admitted for inpatient surgery under Medicare. Per ^[2]. The patient’s medical record indicates sex as “Female.”

1. Locate Box 11 on the UB-04 form, immediately after Box 10 (Birth Date).
2. Enter the single character F – do not add spaces, hyphens, or the word “Female.”
3. Ensure the sex matches the patient’s record at the time of admission.
4. For a Maryland Medicaid outpatient claim, ^[1]. You may leave the field blank if the payer does not require it.
5. If the patient’s sex is unknown and the payer (like Maryland) allows it, enter U.
6. Double-check that no other field (e.g., Patient Name in Box 8b) contradicts the sex entry.
7. Submit the claim. A correctly entered “F” will satisfy Medicare’s requirement; a blank or invalid entry could result in a returned or denied claim.

Common Mistakes & Audit Red Flags

A frequent mistake is leaving Box 11 blank when the payer requires it. ^[2]; missing data can trigger an edit or claim rejection. Another error is using “U” (Unknown) on a Medicare claim, as ^[2]. Providers who ignore this distinction may face audit flags for invalid entry. Conversely, reporting “M” or “F” on a Maryland claim when the sex truly is unknown is inappropriate if the payer accepts “U”; however, ^[1], so leaving it blank is safe. Audit red flags also include sex codes that conflict with the patient’s name or other demographic fields (e.g., Box 8b). Internal consistency is critical. If the sex code is miscoded (e.g., “F” for a male patient), downstream analytics and risk adjustment may be affected. Always verify the sex as recorded in the admission record.

Related Codes/Fields

The following table lists UB-04 fields that are closely related to Box 11 (Patient Sex) and often referenced together for demographic validation.

Field Number	Field Name	Relationship to Box 11	Key Source
08b	Patient Name	Name must align with sex coding; inconsistencies may trigger edits.	[1]
10	Patient Birth Date	Birth date plus sex determine sex-specific medical necessity checks.	[1]
12	Admission/Start of Care Date	Sex is recorded at admission; date must be present for inpatient claims.	[2]
14	Type of Admission	Sex may affect admission type coding in obstetrics or gender-specific services.	[2]
67	Diagnosis Code Principal	Certain diagnoses require sex-specific coding (e.g., pregnancy, prostate cancer).	[2]

Note: The fields above are referenced in the provided source text only where indicated. No additional sources were used.

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References

[1] Maryland Medicaid explicitly lists “U – Unknown” as an acceptable entry — https://health.maryland.gov/mmcp/provider/Documents/ffs-billing/UB04-Hospital-Billing-Instructions%20%281%29.pdf

[2] CMS Chapter 25 indicates that only “M” or “F” are valid for Medicare claims — https://www.cms.gov/regulations-and-guidance/guidance/manuals/downloads/clm104c25.pdf