UB04 Admission Hour Code 01: 01:00 AM - 01:59 AM

Overview

Code 01 in UB-04 Field 13 (Admission Hour) represents the hour of 01:00 AM to 01:59 AM, expressed in military time. This code is part of the admission hour coding system that uses values 00 through 23 to indicate the exact hour of a patient's admission. According to CMS guidelines, "The admission hour code (00-23) represents the hour of admission in military time," with "Code 00 = 12:00 AM (midnight), 01 = 1:00 AM ... 23 = 11:00 PM" ^[1]. The admission hour is a required component on inpatient bills only, as Field 13 captures "the date the patient was admitted for inpatient care or the date outpatient care began" ^[1]. MassHealth adopts the same standard, requiring providers to complete the UB-04 claim form according to CMS specifications ^[2]. Code 01 specifically identifies admissions occurring during the first hour after midnight, which is critical for accurate length-of-stay calculations and reimbursement determinations.

When to Use

Use Code 01 when the patient's admission to inpatient care occurred at any time between 01:00 AM and 01:59 AM. This code applies exclusively to inpatient hospital admissions, as Field 13 is "required on inpatient bills only" ^[1]. The admission hour must be documented in the patient's medical record at the exact time of admission, not when the patient arrived at the emergency department or when orders were written. For example, if a patient is formally admitted to an inpatient bed at 1:15 AM, Code 01 is the correct selection. This code is not used for outpatient services, observation stays that do not convert to inpatient status, or for patients admitted at 12:00 AM (Code 00) or 2:00 AM (Code 02). Providers should ensure the admission hour aligns with the admission date entered in the same field, as both elements together establish the precise start of inpatient care.

Step-by-Step Claim Example

Scenario: A patient is admitted to the hospital at 1:30 AM on March 15, 2024, for acute chest pain.

Step 1: Locate Field 13 on the UB-04 form labeled "Admission/Start of Care Date."

Step 2: Enter the admission date as 03-15-2024 in the date portion of the field.

Step 3: In the two-digit hour box immediately following the date, enter 01 to indicate the admission occurred between 1:00 AM and 1:59 AM.

Step 4: Verify the admission hour matches the medical record documentation. The nursing admission assessment or physician admission order should confirm the time as 1:30 AM.

Step 5: Complete remaining required fields, including Field 14 (Priority of Admission), Field 15 (Source of Admission), and Field 16 (Discharge Hour if applicable).

Step 6: Submit the claim electronically or via paper, ensuring the admission hour code is legible and correctly positioned. MassHealth requires electronic submission unless an approved waiver exists ^[2].

Common Mistakes & Audit Red Flags

Mistake 1: Using Code 01 for midnight admissions. Code 00 represents 12:00 AM (midnight), not Code 01. Using Code 01 for a 12:30 AM admission is incorrect and may trigger claim denials or audits ^[1].

Mistake 2: Confusing admission hour with arrival time. The admission hour must reflect when the patient was formally admitted as an inpatient, not when they arrived at the emergency department. Using the ED arrival time instead of the actual admission time is a common error that can lead to incorrect length-of-stay calculations.

Mistake 3: Leaving the admission hour blank. Field 13 requires both the date and hour for inpatient claims. Omitting the hour code may result in claim rejection or processing delays.

Audit Red Flags: Payers may flag claims where the admission hour is consistently 01 for all overnight admissions, suggesting systematic coding errors. Additionally, claims with admission hour 01 but discharge hour showing a very short length of stay (e.g., discharge at 02:00 AM the same day) may trigger medical necessity reviews. MassHealth and other payers expect the admission hour to match clinical documentation precisely ^[2].

Related Codes/Fields

Code/Field	Description	Relationship to Code 01
Code 00	12:00 AM - 12:59 AM	Adjacent hour; use for midnight admissions only
Code 02	2:00 AM - 2:59 AM	Adjacent hour; use for 2 AM admissions
Field 14	Priority of Admission	Indicates admission type (emergency, urgent, elective)
Field 15	Source of Admission	Identifies referral source (physician, clinic, transfer)
Field 16	Discharge Hour	Records hour of discharge in military time format
Field 12	Patient Control Number	Internal tracking number for the claim
Field 17	Patient Discharge Status	Identifies discharge destination (home, transfer, expired)

All admission hour codes follow the same military time format as Code 01, with values ranging from 00 (midnight) through 23 (11:00 PM) ^[1].

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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