UB04 Admission Hour Code 99: Unknown

Overview

The Admission Hour Code field (FL 13 on the UB‑04) indicates the hour of a patient’s admission or start of care. According to CMS guidance, codes 00 through 23 are defined in military time (00 = 12 AM, 01 = 1 AM, …, 23 = 11 PM) ^[1].

Code 99 is not mentioned in any of the provided source documents. The CMS transmittal lists only codes 00‑23, and the MassHealth UB‑04 Billing Guide (February 2021) does not include a valid code 99 for admission hour ^[2]. Because neither source defines or authorizes code 99, its meaning of “Unknown” cannot be confirmed using the materials supplied.

In normal UB‑04 billing, admission hour codes are mandatory for inpatient claims only; outpatient bills may leave the field blank or use a code as required by the payer. If a provider encounters a patient whose exact admission hour is unavailable, the appropriate action should be determined by the payer’s specific instructions. Without payer‑sanctioned documentation of code 99, billing systems should default to the nearest estimated hour and maintain supporting clinical records.

When to Use

Since code 99 is absent from the provided sources, it should not be used on claims submitted to Medicare or MassHealth based on these guidelines.

• CMS standard: Only codes 00‑23 are acceptable for the admission hour ^[1].
• MassHealth requirement: The MassHealth UB‑04 guide references “Code Sets for the UB‑04 Claim Form” (see page 23 of the guide), but the available excerpt does not list a 99 code for admission hour ^[2].

Therefore, code 99 should not be billed to any payer that follows the UB‑04 specifications as outlined in these federal and state references. If a provider believes “Unknown” is acceptable for a particular payer, they must first obtain written confirmation from that payer and verify that code 99 is valid in their electronic or paper claim system.

In practice, most payers require an hour code because it is used for date‑of‑service logic, utilization review, and length‑of‑stay calculations. When the exact admission hour is missing, the admitting department should document the approximate time and use the best estimated code (e.g., 12 for noon if the time is unknown but the date is the same). This avoids the risk of a rejected or incorrectly‑processed claim.

Step-by-Step Claim Example

Because code 99 is not supported by the provided sources, an example using this code cannot be constructed from the available material. Below is a standard scenario using only codes 00‑23.

Scenario: A patient is admitted to the hospital on 05/15/2025 at 9:45 AM. The admission hour code would be 09 (military 9 AM).

Field	Value	Source
FL 13 – Admission Date	05/15/2025	[1]
FL 13 – Admission Hour	09	[1]
FL 13 – Type of Admission	1 (Emergency)	(standard UB‑04)

If the admission hour were truly unknown, the provider would need to request a payer exception. Without a documented payer allowance for code 99, the example cannot be completed.

Common Mistakes & Audit Red Flags

• Using code 99 when not allowed: On claims submitted to Medicare or MassHealth, code 99 may be rejected as invalid because it is not defined in the source transmittal or billing guide. This can cause a denial or “missing/invalid” edit ^[1].
• Leaving field blank when hour is unknown: CMS requires an admission hour for inpatient bills. A blank field is often treated as an error, even if the hour is uncertain ^[1].
• Documentation mismatch: If the medical record indicates a specific time (e.g., 14:32) but the claim uses 99, auditors may flag a discrepancy. Always use the documented hour, rounding to the nearest whole hour when necessary.
• Failure to consult payer specifications: Some payers may have proprietary extra codes beyond 00‑23. Using 99 without prior written authorization can lead to a claim rejection. The MassHealth guide emphasizes reviewing payer‑specific instructions ^[2].

Providers should ensure their billing system does not automatically insert code 99 as a default for missing hour data. Routine audits should verify that all inpatient claims contain a valid hour code (00‑23).

Related Codes/Fields

Code / Field	Description	Source
FL 13 – Admission Date	Date patient was admitted or outpatient care began (MMDDYYYY). For inpatient only.	[1]
FL 13 – Admission Hour Code 00‑23	Military‑time hour of admission. 00 = 12 AM, 01 = 1 AM, ..., 23 = 11 PM.	[1]
FL 13 – Type of Admission	Code indicating urgency (1=Emergency, 2=Urgent, 3=Elective, etc.); required on inpatient bills.	Standard UB‑04
FL 14 – Priority (Type) of Visit	Outpatient visit type (e.g., 1=Emergency, 2=Urgent, 3=Elective).	Standard UB‑04
FL 15 – Point of Origin for Admission or Visit	Codes for patient source (e.g., physician referral, transfer).	Standard UB‑04

Important: Code 99 does not appear in any of the provided source documents and cannot be associated with these fields based on the available references.

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References

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

[2] MassHealth UB-04 Guide — https://www.mass.gov/doc/ub-04-billing-guide-0/download