HCPCS & CPT Modifiers for Drug Billing
Last reviewed: May 2, 2026 by Catherine Rose, CPC
A working reference for the modifiers that actually appear on specialty drug claims — what each one means, when it applies, when it doesn’t, and the 2026 rule changes that have been catching practices off guard. Scoped to drug billing under Medicare Part B and commercial payers; if you’re looking for surgical-modifier or anesthesia-modifier references, this isn’t that.
How to use this reference. Click a modifier code for the deep-dive page. Each page leads with a quick-answer box (so you can ship the claim), then drills into edge cases, denials, and the 2026 rule changes. Worked examples use real J-codes from our drug library so you can check your own math.
Drug waste — single-dose containers
JZ
Zero drug amount discarded
Required on Medicare Part B claims for single-dose-container drugs when no drug was discarded. Edits started enforcing claims in 2024. Most common modifier on adult flat-dose drugs (Ocrevus, Briumvi, Keytruda).
Read the JZ deep-dive →
JW
Drug amount discarded / wasted
Used on the wasted units of a single-dose vial when discarded amount is documented. Pairs with JZ on the not-wasted units (separate claim line). Eligible for the manufacturer refund process under Section 1847A(h).
Read the JW deep-dive →
Administration route
JA
Intravenous administration
For drugs with both IV and SC formulations under one HCPCS code. Identifies the IV route. Common with rituximab and infliximab biosimilars.
Coming soon
JB
Subcutaneous administration
Companion to JA for the SC formulation. Pricing and units may differ from the IV form despite a shared HCPCS root. Read this before billing rituximab Hycela or infliximab SC.
Coming soon
ABN & medical-necessity
GA
ABN issued, expected denial
Indicates an Advance Beneficiary Notice (ABN) was issued because the service is expected to be denied as not medically necessary. Patient acknowledged liability.
Coming soon
GZ
No ABN, expected denial
Used when the service is expected to be denied but no ABN was issued. Practice absorbs the cost — cannot bill the patient. The biller’s "I should have issued the ABN" modifier.
Coming soon
GY
Statutorily excluded
Item is statutorily excluded from Medicare coverage. Forces a denial that the patient’s secondary may pick up. Different from GZ — this is a "Medicare doesn’t cover this category at all" signal.
Coming soon
KX
Documentation requirements met
Attests that documentation supporting medical necessity is on file. Required on many specialty-drug claims (immunoglobulins, growth hormones) where LCD criteria apply.
Coming soon
Site of service & component
PO
Excepted off-campus PBD
Service furnished at an excepted off-campus provider-based department. Determines hospital outpatient payment under Section 603 of the Bipartisan Budget Act.
Coming soon
PN
Non-excepted off-campus PBD
Non-excepted services furnished at an off-campus PBD. Pays at the lower OPPS-equivalent rate. Shows up on infusion-center claims a lot.
Coming soon
TC / 26
Technical / professional component
Splits a service into the technical (TC) and professional (26) component. Limited applicability for drug billing — most specialty drug administration is whole-claim.
Coming soon
RT / LT
Right / left side
Anatomic-side modifiers. Show up on intravitreal injection claims (Eylea, Lucentis, Vabysmo). Bilateral injections require two claim lines with RT and LT respectively, not modifier 50.
Coming soon
Distinct service / unbundling
25
Significant, separately identifiable E/M
Indicates an E/M service was significant and separate from the procedure performed the same day. Routinely required when billing an office visit alongside a same-day infusion.
Coming soon
59
Distinct procedural service
Identifies a procedure as distinct from another service performed the same day. NCCI edits sometimes pair drug administration codes — modifier 59 unbundles them when documentation supports.
Coming soon
Why we maintain this reference
CMS modifier rules change every year. Manufacturer refund rules under Section 1847A(h) of the Social Security Act started enforcing in 2024 and have continued to evolve. Payer policies layer on top — one payer may require KX where another doesn’t. We update this reference quarterly against the CMS Internet-Only Manuals and the MLN Matters articles, and on an event-driven basis when a payer policy or rule change crosses our reader-feedback channel. Catherine Rose, CPC reviews each modifier page on publication and on each material update; the full process is in the Editorial Policy.