UB04 Field 46: Units of Service

Overview

Field 46 (Box 46) on the UB‑04 claim form captures the Units of Service for each revenue‑code line. It is required for both inpatient and outpatient hospital claims, as confirmed by the Maryland Medicaid UB‑04 billing instructions (listing FL 46 as mandatory) ^[1] and by CMS Transmittal R1915CP, which explicitly states “FL 46 - Units of Service Required” ^[2]. The entries in this column quantify the services reported under each revenue code category. For example, accommodation‑type revenue codes show the number of days, while non‑accommodation codes such as blood or drugs show pints or doses. When a HCPCS code is required on the line, the units equal the number of times the procedure or service was performed ^[3]. Accurate reporting of units is essential because it directly affects reimbursement and is a key data element for utilization review.

When to Use

Field 46 must be completed on every service line (lines 1–23) of the UB‑04 form. It is used whenever a revenue code is entered in Box 42. The quantity reported depends on the nature of the service. For room and board (revenue codes 010x–020x), units represent census days – the number of days the patient occupied that type of accommodation. For ancillary services such as blood (revenue code 03xx), units reflect the number of pints or units transfused. For pharmacy items, units may be doses, tablets, or milliliters as defined by the revenue code. When a HCPCS code is present in Box 44, the units in Field 46 must equal the number of times that specific procedure or service was performed, not a time‑based unit unless the HCPCS itself is time‑based (e.g., 15‑minute increments) ^[3]. The requirement applies to all payer types, including Medicare, Medicaid, and commercial insurers. The Maryland Medicaid instructions treat Field 46 as mandatory for both inpatient and outpatient claims ^[1]. If a service line has zero units, the line should generally not be submitted; otherwise, the claim may be rejected or subjected to auditor scrutiny.

Step-by-Step Claim Example

Scenario: A patient is admitted for three days (inpatient), receives two units of packed red blood cells, and has a single outpatient diagnostic colonoscopy (HCPCS G0105) performed once.

Step 1 – Inpatient Accommodation: On line 1, enter revenue code 0110 (medical/surgical general) in Box 42. In Box 46, enter 3 (the number of days). The source for this practice is the CMS Chapter 25 description that “units for accommodation revenue codes represent number of days” ^[3].

Step 2 – Blood: On line 2, enter revenue code 0381 (blood). In Box 46, enter 2 (pints). The same CMS guidance notes that for non‑HCPCS services like blood, units follow the revenue code category (e.g., pints) ^[3].

Step 3 – Outpatient Procedure: On line 3 (outpatient claim), enter revenue code 0490 (ambulatory surgical care) in Box 42, and HCPCS code G0105 in Box 44. Since a HCPCS is required, the units in Box 46 must equal the number of times the service was performed – in this case 1. CMS specifies: “when HCPCS codes are required for services, the units are equal to the number of times the procedure/service being reported was performed” ^[3]. All three lines are required per the Maryland and CMS mandates for Field 46 ^{[1] [2]}.

Common Mistakes & Audit Red Flags

Several errors in Field 46 can trigger denials or audits:

• Missing units: Omitting the field entirely is a common mistake, but CMS and Maryland both require it on every service line ^{[2] [1]}.
• Incorrect unit type: Reporting days instead of pints for blood, or reporting hours when the revenue code calls for a count, is a major red flag. The CMS guidance warns that units must match the revenue code category ^[3].
• Zero units: Submitting a line with “0” in Field 46 is audit‑prone because it implies no service was rendered. Providers should remove such lines.
• Mismatched HCPCS units: When a HCPCS code is present, units must equal the number of procedures performed. For example, if a bilateral procedure is reported with HCPCS modifier 50 but only one unit is entered, the claim may be underpaid or rejected.
• Inpatient/outpatient inconsistency: Using the same unit logic for both settings can cause problems. Inpatient days are calendar days; outpatient units are typically procedure counts. The Maryland instructions treat Field 46 as required irrespective of setting, but the unit definition differs ^[1].
• Revenue code/unit conflict: An accommodation line (revenue code 0100) with units of “1” for a three‑day stay will be flagged. Auditors cross‑check admission/discharge dates against accommodation units.

Related Codes/Fields

Field 46 does not operate in isolation. It interacts with several other fields on the UB‑04 form. The table below lists the most relevant related fields and their relationship to Units of Service.

Field / Box	Name	Relationship to Field 46
42	Revenue Code	Defines the category of service; determines whether units are days, pints, doses, or counts. Units must align with revenue code meaning [3].
44	HCPCS / RATE / HIPPS Code	When a HCPCS code is entered, Field 46 must equal the number of times the procedure was performed [3].
45	Service Date	The date of service for the line. For inpatient accommodation lines, the service date is the admission date, and units reflect days covered. For outpatient, the date relates to the procedure performed multiple times.
47	Total Charges	Calculated as units × unit charge (or as defined by revenue code). A mismatch between Field 46 units and total charges is a common audit flag.
48	Non‑Covered Charges	When a line has non‑covered charges, Field 46 units still must be reported. Units apply to both covered and non‑covered portions.

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References

[1] Maryland Medicaid — FL 46 — https://health.maryland.gov/mmcp/provider/Documents/ffs-billing/UB04-Hospital-Billing-Instructions%20%281%29.pdf

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

[3] CMS Chapter 25 — FL 46 — https://www.cms.gov/regulations-and-guidance/guidance/manuals/downloads/clm104c25.pdf