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Descriptors and administrative fields exactly as published in the CMS HCPCS quarterly file.
Billing context: C-codes
Units are reported in multiples of the dosage in the code descriptor.
One HCPCS billing unit of C1821
The descriptor does not state a numeric dosage per unit.
| Setting | Max units / day | Adjudication (MAI) | CMS rationale |
|---|---|---|---|
| Practitioner services (professional claims) | 4 | 3 Date of Service Edit: ClinicalDate-of-service edit (clinical benchmarks): more units for the same patient and date are possible but medically highly unlikely; documentation of medical necessity may be considered. | Clinical: CMS Workgroup |
| Facility outpatient hospital services | 4 | 3 Date of Service Edit: ClinicalDate-of-service edit (clinical benchmarks): more units for the same patient and date are possible but medically highly unlikely; documentation of medical necessity may be considered. | Clinical: Data |
An MUE is the most units CMS expects for this code for one patient on one date of service by the same provider in most correctly reported claims. CMS MUE program
Medicare Part B drug payment limits per billing unit, by quarter, from the CMS payment limit (ASP) files.
No authoritative public data was located for this field. CMS did not publish a Part B payment limit for C1821 in the quarters imported.
No authoritative public data was located for this field.
Medicare hospital outpatient (OPPS) · Q4 2026
N Packaged: no separate payment
Washington Apple Health · professional claims
Not on HCA's professional administered drug fee schedule.
AAC = actual acquisition cost, based on NDC or invoice; BR = by report; NC = not covered; DC = not covered, see a different code; DP = covered under another program (see comments); PA = prior authorization; EPA = expedited prior authorization (see the billing guide); CPA = contractor prior authorization (Qualis). For professional claims; hospital-administered drugs are paid under HCA's outpatient (OPPS/EAPG) rules.
Packages CMS assigns to this code in its NDC–HCPCS crosswalks, with billable units per package. Only official crosswalk rows are shown.
No CMS NDC–HCPCS crosswalk rows were located. CMS notes its crosswalks are not a comprehensive list of all NDCs.
Medicare coverage is set nationally (NCDs) and by each Medicare Administrative Contractor (LCDs and Billing & Coding articles). These links open the official documents.
Verification neededCodeRx links to coverage documents instead of copying them: CMS distributes their code lists under AMA, ADA, and AHA license terms that limit reuse. Medicare Advantage, Medicaid, and commercial plans set their own coverage and prior-authorization rules.
Changes detected between the CMS quarterly HCPCS files CodeRx has imported.
| Quarterly file | Change | CMS action code | Details |
|---|---|---|---|
| Q1 2023 | In earliest ingested file | N — No maintenance | Added date Jan 1, 2007 |
All imported releases, checksums, and import reports are listed on the data sources page.
Disclaimer. This application provides informational coding and reimbursement reference data. It does not constitute legal, clinical, coding, or billing advice. Codes, payment amounts, payer rules, and coverage policies can change. Verify all information with current CMS publications, the applicable payer, and your organization’s compliance policies before submitting a claim. CodeRx is not affiliated with or endorsed by CMS, FDA, Medicare, or any payer.