UB04 Admission Hour Code 21: 09:00 PM - 09:59 PM

Overview

Code 21 on the UB-04 claim form represents the admission hour of 09:00 PM to 09:59 PM, corresponding to military time 21:00. This code is used in Field 13 (Admission/Start of Care Date) to indicate the specific hour when a patient was admitted for inpatient care or when outpatient care began. According to CMS guidelines, the admission hour code must be a two-digit number from 00 to 23, where 00 represents 12:00 AM (midnight), 01 represents 1:00 AM, and so on through 23 representing 11:00 PM ^[1]. The code 21 specifically indicates that admission occurred during the 21st hour of the day, which is the hour beginning at 9:00 PM and ending at 9:59 PM. This code is essential for accurate billing and medical record documentation, as it helps payers determine appropriate reimbursement levels and verify the timing of services provided.

When to Use

Code 21 should be used when a patient's admission or start of care occurs at any point between 9:00 PM and 9:59 PM, regardless of the specific minute within that hour. This applies to both inpatient admissions and outpatient care starts. For example, if a patient is admitted to the hospital at 9:15 PM, the admission hour code would be 21. Similarly, if outpatient observation services begin at 9:45 PM, code 21 would be appropriate. The code must be entered in Field 13 of the UB-04 claim form, which is required on inpatient bills only, though it may also be used for outpatient care start dates ^[1]. Providers should ensure that the admission hour code matches the actual time documented in the patient's medical record to maintain consistency and avoid billing discrepancies. This code is particularly relevant for emergency department admissions that occur during evening hours, as many hospitals experience peak admission times during this period.

Step-by-Step Claim Example

Scenario: A patient is admitted to the hospital at 9:30 PM on March 15, 2024, for an acute myocardial infarction.

Step 1: Complete Field 12 (Admission Date) with the date of admission: 03/15/2024.

Step 2: Complete Field 13 (Admission Hour) with code 21, representing 09:00 PM - 09:59 PM. Enter "21" in the two-digit field.

Step 3: Complete Field 14 (Priority of Admission) with the appropriate code (e.g., 1 for emergency, 2 for urgent, 3 for elective).

Step 4: Complete Field 15 (Source of Admission) with the appropriate code (e.g., 1 for physician referral, 2 for clinic referral, 7 for emergency room).

Step 5: Complete Field 16 (Discharge Hour) if applicable, using military time (e.g., 14 for 2:00 PM discharge).

Step 6: Complete remaining required fields including patient demographics, insurance information, diagnosis codes, and procedure codes.

Step 7: Submit the claim electronically or via paper, ensuring all fields are accurate and consistent with medical records.

Example Claim Data:

• Field 12: 03/15/2024
• Field 13: 21
• Field 14: 1 (Emergency)
• Field 15: 7 (Emergency Room)
• Field 16: (Leave blank if not discharged yet)

Common Mistakes & Audit Red Flags

Mistake 1: Using incorrect military time conversion. Providers sometimes confuse 9:00 PM with 9:00 AM, entering code 09 instead of 21. This is a common error that can lead to claim denials or payment delays. Always verify that evening hours use codes 12-23.

Mistake 2: Failing to match admission hour with medical records. If the medical record shows admission at 9:30 PM but the claim shows code 09 (9:00 AM), auditors will flag this as a discrepancy. This can trigger medical necessity reviews or fraud investigations.

Mistake 3: Using code 21 for admissions that occur at 10:00 PM or later. Code 21 only covers 9:00 PM to 9:59 PM. Admissions at 10:00 PM require code 22. Using the wrong hour code can result in incorrect reimbursement calculations.

Mistake 4: Leaving Field 13 blank or using non-numeric characters. The field requires a two-digit numeric code from 00-23. Blanks or alphabetic characters will cause the claim to be rejected.

Audit Red Flags:

• Multiple claims with the same admission hour for different patients on the same day
• Claims showing admission hour 21 for outpatient services that typically occur during daytime hours
• Inconsistent admission hours compared to facility patterns (e.g., a surgical unit rarely admitting at 9 PM)
• Claims with admission hour 21 but no corresponding emergency department or after-hours documentation

Related Codes/Fields

Code/Field	Description	Relationship to Code 21
Field 12	Admission Date	Required companion field; date must match the hour code
Field 14	Priority of Admission	Indicates urgency (emergency, urgent, elective)
Field 15	Source of Admission	Shows referral source (physician, clinic, ER)
Field 16	Discharge Hour	Used for inpatient stays; must be later than admission hour
Code 20	08:00 PM - 08:59 PM	Preceding hour; used for admissions at 8 PM
Code 22	10:00 PM - 10:59 PM	Following hour; used for admissions at 10 PM
Code 00	12:00 AM - 12:59 AM	Midnight hour; used for admissions at midnight
Code 12	12:00 PM - 12:59 PM	Noon hour; used for admissions at noon
Field 17	Patient Status Code	Indicates discharge status; may affect billing for same-day admissions

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References

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