Rheumatology Billing Guide 2026: Codes, Infusions and Prior Auth

A rheumatology practice earns most of its money in three places: office visits, infusions, and the drugs given in the infusion suite. Each one has its own billing rules. This guide covers the codes, what Medicare pays for them in 2026, and the mistakes behind most denials.

The rates below are 2026 national Medicare amounts from the CMS fee schedule file. Your local rate will be a little higher or lower. You can check any code for your area in our Medicare fee lookup.

Why Rheumatology Billing Is Hard

• The drugs cost more than the visits. Most practices buy the biologic, give it, then bill for it. This is called buy-and-bill. If the claim denies, the money is already spent.
• Almost every biologic needs prior authorization. Most payers also want proof that cheaper drugs, like methotrexate, were tried first. This is called step therapy.
• Infusion codes are based on time. The start and stop times in the nursing note decide which codes you can bill.

Office Visit Codes and What They Pay in 2026

Many rheumatology follow-ups are 99214 or 99215. These patients often have more than one long-term illness and take drugs that need lab checks. Code what the note supports. Our E/M code level calculator walks through the rules.

Medicare does not pay consult codes (99242 to 99245). For a Medicare patient, bill a new patient visit instead. Some commercial plans still pay consults, so check the plan first.

Infusion and Injection Codes

CPT lets some biologics, such as certain monoclonal antibodies, be billed with the chemotherapy administration codes (96413 and 96415). These pay about twice as much as 96365. Your MAC or payer decides which drugs qualify, so check its list before you bill. If a drug is not on the list, use 96365 and 96366.

These codes have no facility rate. When the infusion happens in a hospital outpatient department, the hospital bills the administration, not the practice.

Joint Injection Codes

• If ultrasound guides the needle, bill the “with ultrasound” code (20604, 20606 or 20611). Do not add a separate ultrasound code. The image must be saved and the note must say ultrasound was used.
• Bill the drug you injected as well, such as J3301 (triamcinolone, per 10 mg) or J1030 (methylprednisolone, 40 mg).
• For both knees, Medicare wants one line with modifier 50. Some commercial plans want two lines with RT and LT instead.
• These codes have a 0-day global period. A visit on the same day needs a separate problem and modifier 25.

Biologic Drug Codes and Units

Bill the drug on its own line, next to the infusion code. The number of units is the dose given divided by the billing unit. For example, a 400 mg dose of infliximab is J1745 with 40 units.

• Wasted drug: Medicare wants modifier JW on a separate line for drug thrown away from a single-dose vial. If none was wasted, add JZ to the drug line.
• NDC numbers: Medicaid and many commercial plans also want the drug's 11-digit NDC on the claim.
• Payment: Medicare pays most Part B drugs at the average sales price plus 6 percent. CMS updates these prices every quarter.
• Self-injected drugs: drugs patients usually inject at home, like adalimumab (Humira) and etanercept (Enbrel), are usually not covered under Medicare Part B. They go through the patient's Part D drug plan.

Diagnosis Codes That Support the Drug

Each biologic is approved for certain conditions. The ICD-10 code on the claim must match one of them and the payer's policy. If it does not, the drug line denies as not medically necessary (CO-50).

• M05.79 Rheumatoid arthritis with rheumatoid factor, multiple sites
• M06.09 Rheumatoid arthritis without rheumatoid factor, multiple sites
• L40.50 Psoriatic arthritis, unspecified
• M45.9 Ankylosing spondylitis, unspecified site
• M32.9 Lupus (systemic lupus erythematosus), unspecified
• M10.9 Gout, unspecified
• M81.0 Age-related osteoporosis without a current fracture
• M35.00 Sjögren syndrome, unspecified

Prior Authorization and Step Therapy

1. Start at least two weeks before the first dose.
2. Send a full package the first time: diagnosis, a disease activity score such as DAS28 or CDAI, lab results, and every drug tried before with dates, doses and why it was stopped.
3. Track the end date and the number of doses approved. Maintenance infusions often run past the approval without anyone noticing.
4. Check again in January. A new plan year often means a new approval.
5. Check the plan's preferred drug. Many plans now want a biosimilar first.
6. If it is denied, ask for a peer-to-peer review with the plan's doctor.

Our prior authorization guide covers the process step by step.

The Denials Rheumatology Practices See Most

A Quick Check Before Every Infusion

• Eligibility and benefits checked for this date of service
• Prior authorization approved, not expired, with doses left
• Drug matches the plan's preferred product (brand or biosimilar)
• Start and stop times in the nursing note
• J-code units match the dose, with JW or JZ added
• NDC on the claim if the plan needs it
• Diagnosis code matches the drug's approved use

When to Get Help

If infusion denials keep coming back, the cause is usually upstream: approvals, units or the plan's drug list. Our rheumatology billing services team handles prior authorization, infusion coding and denial follow-up for practices across the US. It starts with a free one-week audit of your recent claims.

Sources: CMS Physician Fee Schedule (2026 RVU file, conversion factor $33.4009) and CMS ASP drug pricing files. HCPCS drug codes are from the CMS HCPCS Level II code set.