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HCPCS A9521 · Level II · Part B drug

A9521: technetium tc-99m exametazime, HCPCS Level II drug code

Compiled from CMS files by the QuickIntell RCM Editorial Team · Data effective · Method: reference methodology · Report a data correction

Data currency: OPPS Addendum B: October 2026 (effective October 1, 2026); OPPS NDC-HCPCS crosswalk: October 2026 (effective October 1, 2026); NCCI MUE tables: 2026 Q4 (effective October 1, 2026); NCCI PTP edits: v323r0 (2026 Q4) (effective October 1, 2026); ASC Addendum BB (covered ancillary services): October 2026 (effective October 1, 2026). Next CMS release: January 1, 2027 (quarterly update).

Key facts for A9521

Billing unit
up to 25 millicuries
Tc99m exametazime
OPPS payment rate
$927.71
no ASP limit; SI K, October 2026
Practitioner MUE
2
MAI 3
OPPS status
SI K
APC 0766
NCCI exposure
24 col-2 pairs
12% allow a modifier
Coverage articles
0
none list this code

TL;DR

HCPCS A9521 is the Level II code for Technetium tc-99m exametazime, diagnostic, per study dose, up to 25 millicuries, billed per up to 25 millicuries. CMS publishes no ASP payment limit for it; hospital outpatient departments are paid separately under OPPS (status indicator K, $927.71 per billing unit in October 2026). The practitioner MUE allows up to 2 units per date of service (MAI 3). Unlike most diagnostic agents, which OPPS packages into the procedure (status N), A9521 is paid separately in the hospital outpatient department (status K). It is the bundled column-2 code in 24 NCCI pairs, most often with 78018, 78070, 78102. No current Billing and Coding Article lists A9521, so coverage follows the FDA label, compendia and any applicable NCD.

Medicare payment: OPPS rate (no ASP limit)

A9521 does not appear in the October 2026 Part B ASP payment limit file. CMS pays it separately to hospital outpatient departments under OPPS with status indicator K in APC 0766, at a national unadjusted rate of $927.71 per up to 25 millicuries. Status K is a separately paid, non-pass-through drug or biological, including therapeutic radiopharmaceuticals. In a physician office the Medicare contractor prices the drug, often from invoice; commercial and Medicaid payers set their own rates.

NDC to HCPCS billing-unit conversion

The October 2026 OPPS crosswalk lists no NDC for A9521. Report the NDC from the product label and confirm the units conversion from the HCPCS descriptor (Technetium tc-99m exametazime, diagnostic, per study dose, up to 25 millicuries).

Medically Unlikely Edits (MUE)

CMS publishes 2 MUE values for A9521. For practitioners the limit is 2 units per date of service with adjudication indicator 3, a date-of-service clinical edit: units above the limit deny but can be paid on appeal with documentation that the quantity was medically reasonable.

MUE values for A9521 by setting
SettingMUE (units/DOS)MAICMS rationale
Practitioner services23 Date of Service Edit: ClinicalCode Descriptor / CPT Instruction
Facility outpatient hospital23 Date of Service Edit: ClinicalCode Descriptor / CPT Instruction

MUE for A9521 in every setting opens the lookup with this code filled in, next to any other code on the same claim.

NCCI edits and add-on relationships

In the practitioner PTP file v323r0 (effective October 1, 2026), A9521 is the column-2 code in 24 active pairs, 12% of which allow a modifier (indicator 1), and the column-1 code in 1. 12 historical pairs have been deleted over time. CMS's most frequent rationale: Misuse of Column Two code with Column One code.

When billed with these column-1 codes, A9521 is the bundled component unless the pair allows a modifier and the documentation supports a distinct service.

Column-1 codes most often paired with A9521
Column-1 codePairs
78018 (CPT; descriptor licensed by AMA)1
78070 (CPT; descriptor licensed by AMA)1
78102 (CPT; descriptor licensed by AMA)1
78103 (CPT; descriptor licensed by AMA)1
78122 (CPT; descriptor licensed by AMA)1
78140 (CPT; descriptor licensed by AMA)1
78215 (CPT; descriptor licensed by AMA)1
78226 (CPT; descriptor licensed by AMA)1
78227 (CPT; descriptor licensed by AMA)1
78300 (CPT; descriptor licensed by AMA)1

These codes are considered components of A9521 when reported together on the same date of service.

Column-2 codes most often bundled into A9521
Column-2 codePairs
A9512 Tc99m pertechnetate1

The counts above are exposure, not answers for a specific claim. Check A9521 against another code to see whether a given pair bundles, which code is paid and whether a modifier can separate them.

A9521 is neither an add-on code nor a designated primary code in the 2026 Q4 NCCI add-on edit file.

Medicare coverage articles

No current Billing and Coding Article lists A9521 in its HCPCS table. Coverage then follows the drug's FDA label, compendia and any National Coverage Determination; check the Medicare Coverage Database before administering off-label.

Hospital outpatient (OPPS) status

In the October 2026 OPPS Addendum B, A9521 carries status indicator K and is assigned to APC 0766, with a published national unadjusted payment of $927.71. Status K means the drug is paid separately under OPPS rather than packaged into the procedure.

Common denials for A9521 and how to prevent them

CARC 16 · M119

NDC missing, invalid or not matched to the HCPCS code

CARC 151 · N362

units billed exceed the MUE for the date of service

CARC 50 · N115

diagnosis not covered by the applicable coverage article or LCD

How QuickIntell checks A9521 before the claim leaves

QuickCode validates the NDC-to-unit conversion against the current OPPS NDC-HCPCS crosswalk, checks units against every published MUE setting and flags PTP and add-on conflicts on the same claim. QuickRCM routes CARC 16, 151 and 50 denials on drug lines with the matching coverage article attached so the appeal starts with evidence.

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Frequently asked questions — HCPCS A9521

What does HCPCS code A9521 describe?

A9521 is defined by CMS as "Technetium tc-99m exametazime, diagnostic, per study dose, up to 25 millicuries". Each billing unit represents up to 25 millicuries, so the units reported on the claim must equal the dose administered divided by that unit.

Is A9521 a CPT code?

No. A9521 is a HCPCS Level II code, the letter-plus-four-digit set CMS maintains for drugs such as technetium tc-99m exametazime; CPT codes are five-character codes maintained by the AMA. On a Part B claim A9521 reports the drug itself in up to 25 millicuries units, and the administration is billed on its own line.

What does Medicare pay for A9521 in a hospital outpatient department?

A9521 has no Part B ASP limit; the October 2026 OPPS Addendum B pays it separately under status K, APC 0766, at $927.71 per up to 25 millicuries.

How many units of A9521 can be billed per day?

The practitioner Medically Unlikely Edit is 2 units per date of service with adjudication indicator 3 (Date of Service Edit: Clinical). MAI 3 edits can be appealed with documentation that the units were medically reasonable. CMS cites "Code Descriptor / CPT Instruction" as the rationale.

Does A9521 have NCCI bundling edits?

In the v323r0 practitioner PTP file, A9521 appears as the column-2 (bundled) code in 24 active pairs and as the column-1 code in 1. 12% of the column-2 pairs allow a modifier (indicator 1). The most frequent column-1 partners are 78018, 78070, 78102, 78103, 78122, and CMS's leading rationale is "Misuse of Column Two code with Column One code".

Sources

Every figure on this page is taken from the CMS publications below, as released by the Centers for Medicare & Medicaid Services. Projection built 2026-10-10. Verify against the primary file before billing or contracting decisions. The reference methodology explains how each figure is computed from these files.

Disclaimer

This page is an operational reference compiled from CMS publications: the Medicare Part B drug payment limit and NDC crosswalk files, NCCI MUE and add-on edit tables, aggregate PTP statistics, OPPS Addendum B, ASC Addendum BB and the Medicare Coverage Database. Payment limits and rates are Medicare national amounts; commercial and Medicaid payers differ. CPT codes are shown as numbers only; CPT descriptors are copyright AMA. Nothing here is legal, clinical or billing advice.

Found a figure that does not match the CMS file? Report a data correction with the CMS file and the value you expected; the request reaches the editorial team through the contact form.