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HCPCS Q9998 · Level II · Part B drug

HCPCS Q9998: Injection, ustekinumab-aekn (selarsdi), biosimilar, 1 mg

Reviewed by QuickIntell RCM Editorial Team · Last reviewed

Data effective
Data currency: ASP payment limits October 2026 (effective October 1, 2026); MUE and NCCI edits 2026 Q4 (effective October 1, 2026); OPPS Addendum B July 2026 (effective July 1, 2026). Next CMS release: January 1, 2027 (ASP, MUE, NCCI and OPPS quarterly updates).

Key facts for Q9998

Billing unit
1 MG
Inj ustekinumab-aekn, 1 mg
ASP payment limit
$10.48
October 2026; -0.5% vs July 2026
Practitioner MUE
520
MAI 3
OPPS status
SI G
APC 0859
NCCI exposure
no PTP pairs
Coverage articles
0
none list this code

TL;DR

HCPCS Q9998 is the Level II code for Injection, ustekinumab-aekn (selarsdi), biosimilar, 1 mg, billed per 1 MG. The Medicare Part B ASP payment limit for October 2026 is $10.48 per billing unit, down 0.5% from July 2026. The practitioner MUE allows up to 520 units per date of service (MAI 3). Under OPPS it carries status indicator G in APC 0859. As a biosimilar it has its own code and ASP; the reference product cannot be billed under this code, and the JZ or JW modifier rules for discarded amounts apply per single-dose vial. With a 1 mg billing unit, a single administration can be hundreds of units; the unit count on the claim must equal the milligrams given, and rounding rules for partial units follow the contractor's guidance. The ASP crosswalk maps 8 NDCs to it, sold as Ustekinumab-AEKN, Selarsdi by Nupathe Inc. No current Billing and Coding Article lists Q9998, so coverage follows the FDA label, compendia and any applicable NCD.

Medicare Part B payment limit (ASP)

CMS sets the Part B payment limit for Q9998 at $10.48 per 1 MG for October 2026, derived from manufacturer average sales price plus 6%, compared with $10.529 in July 2026. Beneficiary coinsurance is 20%.

ASP payment limits for Q9998
QuarterPayment limitPerCoinsurance
October 2026$10.481 MG20%
July 2026$10.5291 MG—
CMS note: "lesser of" methodology applied

NDC to HCPCS billing-unit conversion

The October 2026 ASP crosswalk maps 8 NDCs from 1 labeler to Q9998. Report the NDC in the claim's drug segment and bill the number of Q9998 units that equals the quantity administered divided by 1 MG; the last column gives units per full package.

NDCs that crosswalk to Q9998
NDCDrug nameLabelerPackage sizeBilling units / package
51759-0413-32Ustekinumab-AEKNNupathe Inc0.5 × 145
51759-0414-32Ustekinumab-AEKNNupathe Inc1 × 190
51759-0505-13SelarsdiNupathe Inc0.5 × 145
51759-0505-32SelarsdiNupathe Inc0.5 × 145
51759-0607-32SelarsdiNupathe Inc1 × 190
51759-0708-13SelarsdiNupathe Inc26 × 1130
51759-0709-32Ustekinumab-AEKNNupathe Inc0.5 × 145
51759-0710-32Ustekinumab-AEKNNupathe Inc1 × 190

Medically Unlikely Edits (MUE)

CMS publishes 3 MUE values for Q9998. For practitioners the limit is 520 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 Q9998 by setting
SettingMUE (units/DOS)MAICMS rationale
Practitioner services5203 Date of Service Edit: ClinicalPrescribing Information
Facility outpatient hospital5203 Date of Service Edit: ClinicalPrescribing Information
DME supplier5203 Date of Service Edit: ClinicalPrescribing Information

NCCI edits and add-on relationships

No active practitioner PTP pair lists Q9998 as a column-1 or column-2 code in v323r0. Drug supply codes are rarely bundled; the administration codes billed with them are where PTP edits usually apply.

Q9998 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 Q9998 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 July 2026 OPPS Addendum B, Q9998 carries status indicator G and is assigned to APC 0859, with a published national unadjusted payment of $10.53. Status G marks pass-through drug payment, which is time-limited.

Common denials for Q9998 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 Q9998 before the claim leaves

QuickCode validates the NDC-to-unit conversion against the current ASP 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.

Explore QuickCodeExplore QuickRCMBook a demo

Frequently asked questions — HCPCS Q9998

What does HCPCS code Q9998 describe?

Q9998 is defined by CMS as "Injection, ustekinumab-aekn (selarsdi), biosimilar, 1 mg". Each billing unit represents 1 MG, so the units reported on the claim must equal the dose administered divided by that unit.

What is the Medicare reimbursement for Q9998 in October 2026?

The ASP-based payment limit is $10.48 per 1 MG, with 20% beneficiary coinsurance. Medicare Administrative Contractors apply this limit; commercial payers use their own fee schedules. The July 2026 limit was $10.529.

How many units of Q9998 can be billed per day?

The practitioner Medically Unlikely Edit is 520 units per date of service with adjudication indicator 3 (3 Date of Service Edit: Clinical). MAI 3 edits can be appealed with documentation that the units were medically reasonable. CMS cites "Prescribing Information" as the rationale.

Which NDCs map to Q9998?

The October 2026 ASP crosswalk lists 8 NDCs from 1 labeler: Ustekinumab-AEKN (Nupathe Inc); Selarsdi (Nupathe Inc). For example NDC 51759-0413-32 is a 0.5 package equal to 45 billing units. The crosswalk's billing-units-per-package figure converts each package into Q9998 units.

Does Q9998 have NCCI bundling edits?

No active practitioner PTP pairs list Q9998 as a column-1 or column-2 code in the v323r0 release. Unit limits (MUE) and medical-necessity coverage rules still apply.

Sources

Every figure on this page is taken from the CMS publications below, as released by the Centers for Medicare & Medicaid Services. Projection built 2026-10-01. Verify against the primary file before billing or contracting decisions.

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 and the Medicare Coverage Database. Payment limits 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.