HCPCS code J2326 – Nusinersen (Spinraza) injection billing

Key takeaways

HCPCS code J2326 reports nusinersen at 0.1 mg per unit, so a 12 mg standard-regimen dose is billed as 120 units.

On the high-dose Spinraza regimen, each 50 mg loading dose is 500 units and each 28 mg maintenance dose is 280 units.

J2326 covers only the drug, and Medicare contractor guidance pairs it with CPT 96450 for the spinal puncture on the same date.

Most Medicare Advantage, Medicaid and commercial payers require prior authorization, and a missing or expired PA is a leading cause of denials.

Medicare pays J2326 at ASP plus 6% (about 4.3% after sequestration) in the physician office setting under Part B.

Pabau, the practice management platform we build, keeps billing, payments and invoicing, and reporting in one system beside the patient record.

HCPCS code J2326: Definition, descriptor, and quick reference

HCPCS code J2326 is the Healthcare Common Procedure Coding System Level II code for injection, nusinersen, 0.1 mg. The Centers for Medicare and Medicaid Services maintains it within the J-series drug codes, and it took effect on January 1, 2018. Nusinersen, sold under the brand name Spinraza by Biogen, is an antisense oligonucleotide approved by the FDA for all types of spinal muscular atrophy.

Each unit is 0.1 mg, so a 12 mg standard-regimen dose is billed as 120 units. The high-dose regimen bills 500 units per 50 mg loading dose and 280 units per 28 mg maintenance dose. To check a neighboring J-code before you submit, our HCPCS code reference lists each drug code with its official descriptor.

Eligible diagnoses and ICD-10 codes for J2326

Nusinersen is FDA-approved for spinal muscular atrophy across all four clinical types. The specific ICD-10-CM diagnosis code on the claim must match the patient’s documented SMA classification. According to the CDC/NCHS ICD-10-CM web tool, the primary codes used with J2326 are in the G12 subcategory.

G12.1 is the most frequently billed code because it covers SMA types 2, 3, and 4. Those types account for most patients on ongoing maintenance therapy. Medical necessity documentation must specify which SMA type the patient has. It must also tie that classification to the genetic test result confirming an SMN1 biallelic deletion or point mutation.

Intrathecal administration and companion CPT codes

J2326 reports only the drug. The intrathecal injection is a separate billable service with its own CPT code. Noridian, a Medicare administrative contractor, directs providers to bill J2326 with CPT 96450 on the same date of service. That code covers chemotherapy administration into the central nervous system, requiring and including spinal puncture.

Confirm the payer’s policy before choosing between 96450 and a lumbar subarachnoid injection code. Whichever code you bill, the procedure note must document the spinal puncture and any imaging guidance used. Billing J2326 without a companion procedure code is a common error that triggers automatic claim edits at most payers.

J2326 billing units: Calculating the correct unit count

Each J2326 unit is 0.1 mg, so the unit count is the dose in milligrams multiplied by 10. Billing one unit for a 12 mg dose pays for roughly 1/120th of the drug. That underpayment often surfaces only at reconciliation, weeks after the claim went out. The chart below shows the count to enter for each dose across both regimens.

Step-by-step unit calculation

1. Identify the dose administered: The standard regimen uses 12 mg per injection, delivered in one vial (5 mL solution at 2.4 mg/mL). The high-dose regimen uses 50 mg loading doses and 28 mg maintenance doses.
2. Apply the billing unit descriptor: J2326 = 0.1 mg per unit.
3. Divide dose by unit size: 12 mg divided by 0.1 mg = 120 units. The same math gives 500 units for 50 mg and 280 units for 28 mg.
4. Enter the result in the units field: Use 120, 500 or 280 on the CMS-1500 or 837P claim line for J2326.

The standard regimen uses a fixed 12 mg dose, so its claims carry 120 units. A high-dose claim carries 500 units for a loading dose and 280 units for a maintenance dose. Any other unit count needs a documented, payer-approved dose change behind it.

Dosing schedule and expected claim frequency

Spinraza has two FDA-approved regimens, and each sets a different J2326 claim rhythm. Knowing which regimen the patient is on lets coders anticipate frequency edits before they occur.

Payers apply frequency edits to J2326 based on these schedules. Under the standard regimen, a maintenance claim submitted earlier than about 112 days after the prior claim commonly triggers a denial. When the date falls close to that threshold, include the prior administration date and the PA approval letter to pre-empt an edit.

Ask each payer how it edits the high-dose schedule, because its 14-day loading interval differs from the standard regimen’s.

Place of service codes and their effect on reimbursement

Where the intrathecal injection is performed determines both the applicable CPT companion code rules and the reimbursement methodology for J2326. Three settings are commonly used.

The physician office (POS 11) setting is where coders most often encounter J2326. The outpatient hospital setting introduces OPPS packaging risk. The drug cost may be bundled into the facility’s APC payment rather than separately reimbursed on the professional claim. Neurology practices performing the procedure in an office or infusion suite avoid this complication.

J2326 prior authorization: What payers require

Most Medicare Advantage, Medicaid and commercial payers require prior authorization for HCPCS code J2326. Nusinersen is one of the highest-cost drugs in the neurology formulary, and payers apply rigorous clinical criteria before approving coverage. A missing or expired PA is one of the most common denial reasons after unit errors. Our guide to the prior authorization process walks through the submission and renewal steps.

Clinical documentation typically required for PA

• Confirmed SMA diagnosis with ICD-10-CM code (G12.0, G12.1, or G12.8)
• Genetic testing confirming SMN1 biallelic deletion or point mutation
• Neurologist attestation letter establishing medical necessity
• Baseline functional assessment scores (CHOP INTEND for infants or HFMSE for older patients)
• Prior administration records if the patient is transitioning from another provider
• Payer-specific PA request form completed by the ordering neurologist

Traditional Medicare generally follows CMS coverage criteria without requiring a formal PA for Part B drug claims. Most Medicare Advantage plans and commercial payers do require one, so confirm the specific payer’s policy before the first administration.

Build PA renewal tracking into your workflow, because maintenance dose authorizations typically expire annually. A lapse causes an immediate denial even when the clinical criteria are unchanged. Insurance eligibility verification before each administration date catches expired authorizations before the injection occurs.

Documentation requirements to support J2326 claims

Medical necessity documentation must connect every element of the claim. Payers auditing J2326 claims look for a clear chain from the genetic diagnosis through the functional assessment to the administration record. A document missing anywhere in that chain produces a denial, even when the clinical picture is straightforward. Our guide to medical billing compliance covers the record-keeping standards behind an audit.

• Office visit note: Documents the SMA diagnosis, current functional status, and the neurologist’s decision to administer nusinersen
• Genetic test result: Laboratory report confirming SMN1 biallelic deletion or point mutation (required by most payers)
• Functional assessment: CHOP INTEND (infants) or HFMSE (older patients) scores at baseline and at each assessment interval
• PA approval letter: Current authorization number, approval date, and expiration date, on file before the claim is submitted
• Drug administration record: Lot number, dose (12 mg, 50 mg or 28 mg), route (intrathecal), date, and administering provider
• Progress notes: Contemporaneous documentation of the procedure and patient tolerance

Medicare reimbursement for nusinersen under Part B

Under Part B, Medicare pays J2326 at ASP plus 6% (about 4.3% after sequestration) in the physician office setting. Payment starts from the drug’s average sales price (ASP) for the current quarter, plus the statutory add-on. The ASP figure changes quarterly. Check the CMS Physician Fee Schedule lookup and the CMS ASP Drug Pricing files on cms.gov for the current J2326 amount. Never rely on a figure from a previous quarter for current claims.

Medicare Part B vs. Part D coverage

J2326 is a Part B drug because a healthcare professional administers it by intrathecal injection. Part D does not cover drugs that fall under Part B, so claims submitted to Part D for nusinersen are rejected. Medicare Advantage plans apply the same Part B benefit, but they may add utilization management requirements beyond traditional Medicare’s criteria.

For a drug at this cost level, every day between administration and claim submission delays a large payment. Streamlined claims management builds the claim from the visit record, so nobody re-keys the dose or the units.

Codes commonly confused with J2326

Several coding errors stem from confusing J2326 with codes for other SMA treatments or for adjacent drug administration services. The table below covers the most frequent points of confusion.

Risdiplam (Evrysdi) is the oral SMA treatment that most frequently causes confusion. Because it treats the same condition as nusinersen, coders sometimes attempt to use J2326 for it. Risdiplam has no HCPCS J-code because patients take it orally at home. It falls under the Part D pharmacy benefit, not the Part B drug benefit. For a broader look at HCPCS Level II code structure, the AAPC Codify HCPCS lookup is a reliable reference.

Why J2326 claims get denied and how to appeal

Nusinersen denials cluster around a predictable set of errors. Understanding the pattern lets billing teams build a pre-submission checklist that prevents most of them. Structured denial management workflows matter most for high-cost drugs, where each unresolved denial holds back a large payment.

Top denial reasons for HCPCS code J2326

• Incorrect units (1 instead of 120, 500 or 280): A one-unit claim pays for only 0.1 mg of drug, and the practice absorbs the balance.
• Missing or expired prior authorization: Maintenance PA typically renews annually. A claim submitted one day after the authorization expires denies on the same basis as one submitted with no PA at all.
• ICD-10 code mismatch: The diagnosis code on the claim differs from the SMA type documented in the PA or clinical notes. G12.0 on the PA approval and G12.1 on the claim generates a mismatch denial.
• Frequency edit exceeded: Standard-regimen maintenance doses submitted fewer than about 112 days apart trigger automatic frequency edits. Include the prior administration date in the submission notes.
• Missing genetic test documentation: Some payers require a copy of the SMN1 confirmation in the initial claim or the PA packet. Absent documentation results in a medical necessity denial.
• No companion CPT code: J2326 billed without CPT 96450, or the injection code the payer accepts, fails claim editing at most payers.

Appeals process for J2326 denials

1. Obtain the explanation of benefits (EOB): Identify the specific denial reason code (CARC) from the ERA or paper EOB.
2. Correct the error if one exists: Unit errors go back as a corrected claim (frequency code 7 on the 837P). Do not appeal an error a corrected claim can fix, because an appeal takes longer to resolve.
3. For medical necessity denials: File a formal redetermination letter including the genetic test result, functional assessment scores, neurologist letter, and PA approval documentation.
4. Track the appeal timeline: Medicare redeterminations must be requested within 120 days of the denial date. Commercial payer timelines vary, typically 30 to 180 days.
5. Escalate to peer-to-peer review: When a commercial payer denies on medical necessity grounds, request a call between its medical director and the treating neurologist. That conversation often resolves a nusinersen denial at this stage.

Medicaid and commercial payer rules for nusinersen

State Medicaid programs and commercial plans apply more variable criteria than traditional Medicare, so each policy needs checking before the first claim.

State Medicaid variability

Each state Medicaid program sets its own coverage policy for nusinersen. Common Medicaid-specific requirements include:

• Age restrictions, since some programs initially limited coverage to pediatric patients
• Functional status thresholds, such as a minimum HFMSE or CHOP INTEND score for continued coverage
• Site-of-care requirements that direct patients to specific infusion facilities

Check the relevant state Medicaid drug policy bulletin or preferred drug list before submitting the first claim for a Medicaid patient.

Commercial payer criteria

Commercial plans typically apply the most restrictive criteria of the three payer categories. Step therapy requirements are uncommon for nusinersen, but commercial plans may require a re-authorization review every six months rather than annually. Some plans impose site-of-care restrictions, preferring infusion centers over physician offices to manage cost. That changes the place-of-service code and can change which companion CPT code the payer accepts.

How Pabau keeps J2326 billing and records together

A clean J2326 claim depends on the dose, the unit count, the PA dates and the procedure note agreeing with each other. In many practices those records live apart. The treatment note sits in the EHR, the authorization letter in a shared drive, and the invoice in a separate billing tool.

In Pabau, the treatment note, digital forms, invoice and payment all sit on the same patient file. Your billing team can check the documented dose against the units on the claim line without switching systems.

Pabau’s reporting pulls invoices and payments into one view, so an underpaid J2326 claim shows up before month-end reconciliation rather than weeks later.

Keep J2326 billing and records in one place

Pabau brings treatment notes, invoicing, payments and reporting into one system. Your billing team can match every J2326 claim to its documented dose before it goes out.

Book a demo

Conclusion

The check that pays back fastest on J2326 is a pre-submission review of units, the companion code and the PA dates. Start with the regimen, because the high-dose schedule changes both the unit count and the claim rhythm.

For practices with several SMA patients on maintenance therapy, the harder work is keeping authorization dates and dose records aligned with each claim. Pabau keeps medical billing, payments and reporting in one system with the patient file, so that check happens in one place.

Book a demo to see how Pabau keeps each J2326 dose, invoice and payment on one patient record.

Continue your research

Need a structured approach to clean claim submission? What makes a clean claim breaks down the elements payers check before processing any drug claim.

Working through an ERA after a J2326 denial? Understanding electronic remittance advice explains how to read CARC and RARC denial codes from the 835 transaction.

Want to understand how billing fits the broader revenue cycle? What is revenue cycle management covers the full claim-to-payment workflow for outpatient practices.

Preparing a PA request for nusinersen? Medical prior authorization form gives you a ready template for the request payers ask for.

Frequently asked questions