HCPCS code J1558 – Xembify immune globulin injection

Key takeaways

HCPCS code J1558 covers Xembify, a 20% subcutaneous immune globulin, billed per 100 mg administered rather than per vial.

Divide the milligrams given by 100 to get units, so a 4 g dose is 40 units of J1558.

Medicare Part B pays J1558 at ASP+6% in the office, and the rate changes every quarter.

Home SCIG for primary immunodeficiency goes to the DME MAC under the Part B DME benefit, not the home infusion therapy benefit.

Most commercial payers and many Medicare Advantage plans require prior authorization, while traditional Medicare relies on LCD coverage criteria.

HCPCS Code J1558: Definition, descriptor, and drug identity

HCPCS Code J1558 is the drug-specific Level II code for 100 mg of Xembify (immune globulin subcutaneous, 20%), given by subcutaneous injection.

It sits in the J-code range of HCPCS Level II, which CMS uses to identify physician-administered drugs outside the CPT framework. Our HCPCS reference for coders covers the rest of the Level II J codes.

If you are new to drug claims, medical billing workflows explains how a code like this moves from the chart to payment.

Code descriptor and classification

The official short descriptor is: Inj immune glob xembify 100 mg. The table below captures the key classification attributes.

Covered drug: Xembify

Xembify is an FDA-approved 20% immune globulin solution manufactured by Grifols. It is the only drug covered under J1558. Key clinical facts coders should know:

• FDA-approved indication: Primary humoral immunodeficiency (PI), including common variable immunodeficiency (CVID), X-linked agammaglobulinemia, and related conditions
• Concentration: 20% (200 mg/mL), making dose-to-unit conversion straightforward
• Route: Subcutaneous only, never intravenous. Billing J1558 for an IV infusion is a coding error
• Generic/INN name: Immune globulin subcutaneous (IgSC), human
• Alternative SCIG products (Hizentra, Cuvitru, HyQvia) each have their own specific J codes and must not be billed under J1558

J1558 billing units: How to calculate and report

J1558 units are billed per 100 mg of Xembify administered, not per vial dispensed. A vial count never belongs in the units field.

Step-by-step unit calculation example

Divide the total milligrams administered by 100 to get the number of units to report.

Rounding rule: Report enough units to cover the dose administered (3,750 mg = 38 units). When the vial is single-dose, report any discarded amount on a separate line with the JW modifier. If none is discarded, Medicare expects the JZ modifier instead. Never report fractional units on a claim line.

Common mistake: Billing 1 unit per vial rather than per 100 mg administered. A single 10 g vial of Xembify yields 100 billable units of J1558. One unit would represent a 100 mg dose, far below a therapeutic infusion. This error almost always triggers a low-payment edit or a units-mismatch denial.

The worked example below follows one dose from the administration note to the claim line, including which contractor receives it.

Medicare reimbursement and fee schedule for HCPCS Code J1558

Medicare Part B reimburses J1558 at Average Sales Price plus 6% (ASP+6%), the standard methodology CMS applies to physician-administered Part B drugs. The payment rate changes every quarter as Grifols reports updated sales data to CMS.

ASP pricing: How CMS sets the rate

ASP is the volume-weighted average price manufacturers charge purchasers, net of discounts and rebates, reported quarterly to CMS. The reimbursement formula is straightforward: ASP + 6% of ASP = payment per 100 mg unit of J1558.

• Quarterly updates: CMS publishes new ASP payment amounts each January, April, July, and October. Always pull the current quarter’s file from the CMS ASP pricing files before billing
• Hospital outpatient vs physician office: Outpatient departments (POS 22) may be reimbursed at a different rate under OPPS/APC methodology rather than ASP+6%. Confirm with the applicable payment system for your setting
• The 6% add-on is meant to offset acquisition, handling and storage costs above the ASP
• Do not state specific dollar figures in patient communications or appeals. The ASP changes quarterly, and a stale rate in a letter can undermine your billing position

To find the current rate, open the current quarter’s ASP file and search for J1558 to confirm the per-unit payment limit.

Medicare and insurance coverage for J1558

Medicare Part B covers subcutaneous immune globulin (SCIG) such as Xembify for primary immunodeficiency (PI) in two ways. In the office, the MAC pays J1558 at ASP+6%. At home, Part B covers it through the DME benefit, billed to the DME MAC. Either way, the patient needs a physician’s order and a covered diagnosis.

Place of service requirements

J1558 is valid across several place of service codes, but coverage rules and payment rates can differ by setting. Run insurance eligibility verification before each infusion to confirm the patient’s plan covers subcutaneous administration in the intended setting.

Home SCIG (POS 12) is billed to the DME MAC under the DME benefit, because the drug is given with an external infusion pump. It does not fall under the Medicare home infusion therapy benefit or the office ASP+6% payment. The DME MAC’s immune globulin Local Coverage Determination (LCD) sets the coverage criteria, so confirm them before submitting.

Prior authorization requirements for J1558

Prior authorization (PA) for J1558 is required by most commercial payers and many Medicare Advantage plans. Traditional Medicare fee-for-service does not require prior authorization for J1558, but MAC LCDs may impose coverage criteria that function as de facto authorization requirements.

Typical PA criteria across commercial payers include:

• Confirmed primary immunodeficiency diagnosis: Documentation of PI (CVID, XLA, or equivalent) with supporting lab values (IgG trough below established threshold)
• Previous IVIG or SCIG treatment history: Many plans require at least one prior course or a prescriber attestation that SCIG is the appropriate route
• Prescriber specialty: Some plans require orders from an allergist/immunologist or relevant specialist
• Step therapy: A small number of plans may require documented IVIG trial first, though this is less common for established SCIG therapy
• Annual renewal: Most PAs are valid for 12 months and require renewal with updated lab values and clinical notes

PA requirements vary by payer and MAC jurisdiction. Do not apply universal rules to every plan. Verify requirements through the payer’s provider portal before each authorization period.

Documentation requirements for J1558 claims

A clean J1558 claim needs a medical record that supports medical necessity and confirms the correct drug and dose. It also carries the NDC that Medicaid and many commercial payers require. Missing any of these elements is enough for a payer to downcode or deny. Clean claim submission for biologics depends on documentation being in the chart before billing runs.

• Diagnosis (ICD-10): Primary immunodeficiency code (see ICD-10 section below) must be present and match the covered indication in the applicable LCD
• Lab results: IgG trough levels documented in the record; many payers use lab thresholds to confirm medical necessity
• Physician order: Written order specifying Xembify, dose in grams, frequency, and route (subcutaneous)
• Drug label/NDC: Xembify NDC from the vial used must be recorded in the administration note
• Dose administered: Actual milligrams given (not prescribed); this drives the unit count on the claim
• Administration note: Date, time, site, lot number, and clinician signature
• Prior authorization number: If applicable, must appear on the claim and match the payer’s records

NDC reporting requirements

Medicaid and many commercial payers require the National Drug Code (NDC) in 11-digit 5-4-2 format. It goes in the shaded area of line 24A on the CMS-1500, with qualifier N4. Medicare Part B physician claims generally do not require it. Recording the Xembify lot number and NDC on the superbill at the point of administration keeps the claim ready for any payer.

Confirm the current Xembify NDC from the FDA DailyMed database before each billing cycle, as NDC numbers can change with new package sizes. NDC reporting on the UB-04 differs by payer, so confirm it in each payer’s billing guide.

J1558 vs similar HCPCS codes: How to choose the right code

Immune globulin has a separate HCPCS J code for nearly every brand, and choosing the wrong one is a fast path to a denial. The determining factors are the specific product administered and the route of delivery.

J1599 and J3590: When an unlisted code applies

J1599 is an IV-only NOS code: “Injection, immune globulin, intravenous, non-lyophilized (e.g. liquid), not otherwise specified, 500 mg.” It would not be used for subcutaneous Xembify, which always takes J1558. An unlisted subcutaneous product with no code of its own goes under J3590, unclassified biologics. An NOS or unclassified code applies only in narrow circumstances:

• A new immune globulin product is FDA-approved but has no specific HCPCS code yet (J1599 for a liquid IV product, J3590 for a subcutaneous one)
• A payer explicitly instructs the provider to use one for a formulary exception request
• The product administered is not Xembify, Hizentra, Gamunex-C, Cuvitru, HyQvia, or any other product with a current specific J code

Submitting J1599 for Xembify reports the wrong route and the wrong unit size, so expect a denial or a mispriced payment.

Common J1558 claim denial reasons and how to fix them

Most J1558 denials fall into six predictable categories. The denial management process for SCIG claims works best when the root cause is found at the billing QA stage. Waiting for the remittance means fixing it after the payer has already said no.

Track denial reasons by code in your practice management system. If J1558 denials cluster around NDC errors or unit counts, the cause sits at the point of administration rather than in billing. Fix the intake workflow, not just the claim. Claims management software that scrubs each claim before submission catches missing fields before the payer does.

ICD-10 diagnosis codes used with J1558

The ICD-10 code on a J1558 claim must match a covered indication in the MAC LCD for immune globulin therapy. Primary immunodeficiency codes in the D80 and D83 series account for the majority of covered diagnoses.

Coverage for secondary immunodeficiencies varies significantly by MAC LCD and payer. Always verify the applicable LCD in the patient’s MAC jurisdiction before billing a secondary immunodeficiency diagnosis with J1558. The AAPC HCPCS code lookup and the PGM Billing HCPCS lookup tool help confirm the current descriptor and billing unit for each immune globulin code.

How Pabau keeps J1558 claims clean before submission

On many infusion teams, authorization dates live in a spreadsheet and units are worked out by hand. A rejected claim then sits in a portal until someone checks it.

Pabau stores each prior authorization as a case and shows how many approved sessions are left. A claim missing its authorization is flagged before it goes out. Claim validation scrubs every CMS-1500 for missing or invalid details, then submits it through Claim.MD.

If a payer rejects the claim, Pabau shows the reason so you can correct it and resubmit. Eligibility checks run before the visit, so coverage problems surface before the drug is given.

Fewer denials, less rework

Pabau tracks prior authorizations as cases, scrubs each claim for missing details, and shows the reason when a payer rejects one. See how it fits immunology and infusion billing.

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Conclusion

J1558 rarely fails on coverage. It fails on the claim line. A vial count lands in the units field, a Medicaid claim goes out without its NDC, or a home dose reaches the wrong contractor.

Fix those at the point of administration and this becomes one of the easier drug claims you file. Record the milligrams given, the NDC and any discarded drug in the note, and bill from that note rather than the order.

The trade-off is a little more charting at the chair for far fewer resubmissions later. Book a demo to see how Pabau tracks authorizations and scrubs J1558 claims before they reach the payer.

Continue your research

Want to reduce claim errors across all your drug codes? Medical billing workflows explained covers the end-to-end process for practice billing teams managing physician-administered drugs.

Dealing with recurring denials on specialty drug claims? Denial management in healthcare walks through root-cause analysis and the appeals workflow for high-cost biologics.

Need a clean-claim checklist for your infusion billing team? Clean claim submission outlines the documentation fields that most often trigger drug-claim edits before they reach the payer.

Billing Gamunex-C or Gammaked instead? HCPCS code J1561 covers the 500 mg immune globulin code used for IV or subcutaneous doses.

Patient switching to HyQvia? HCPCS code J1575 explains the immune globulin and hyaluronidase code billed per 100 mg.

Frequently asked questions