The AY modifier tells Medicare that a service given to an ESRD patient is not for ESRD treatment. It covers lab tests, drugs, supplies, and equipment that could otherwise fall inside the dialysis bundle. Without it, Medicare treats these services as part of the facility payment.
Patients with end-stage renal disease (ESRD) often carry other conditions, such as cancer, diabetes, or heart disease. Tests and drugs for those conditions can look identical to dialysis services on a claim. The AY modifier is how billing teams separate the two for Medicare.
Errors in either direction cost money. A missing modifier can lead to a rejected line, while an unsupported one creates audit exposure. This guide covers the AY definition, correct and incorrect uses, and a claim workflow. It also includes examples, common errors, and the 2026 AX change.
What Is the AY Modifier in ESRD Billing?
The AY modifier is a HCPCS Level II modifier for ESRD patient services not furnished to treat ESRD. CMS introduced it with the ESRD Prospective Payment System (PPS) in January 2011. The PPS pays ESRD facilities a single bundled rate for renal dialysis services.
That bundle includes certain lab tests, drugs, biologicals, equipment, and supplies. CMS calls this arrangement consolidated billing. Under the CMS ESRD PPS Consolidated Billing rules, outside labs and suppliers cannot bill bundled items separately for ESRD treatment.
What the AY Modifier Communicates to Medicare
Placing AY on a claim line sends three specific signals to the Medicare Administrative Contractor (MAC):
- The service has a clinical purpose other than treating the patient’s ESRD.
- The billing provider is requesting payment outside the ESRD PPS bundle.
- The medical record can show that separate purpose if a reviewer asks for it.
Identifying an Unrelated Service vs. Qualifying for Payment
AY identifies an unrelated service, but it does not create payment eligibility on its own. The service must still meet coverage, medical necessity, coding, and frequency rules. Some drugs are classed by CMS as always ESRD-related, and AY cannot pull them out of the bundle.
Practices that rely on outside nephrology billing services should confirm their billers apply this distinction on every claim. A modifier added without support is a compliance problem, even when the claim pays at first.
When Should You Use the AY Modifier?
Use the AY modifier when a service subject to ESRD consolidated billing is furnished for a non-ESRD reason. The documented clinical purpose of the order decides this. The ESRD diagnosis alone never settles the question. Different provider types report AY on different claim formats:
| Provider Type | Where AY Is Reported | Typical Scenario |
|---|---|---|
| Independent or hospital outpatient lab | Part B lab claim line | Blood work ordered for a cancer workup |
| ESRD facility | Type of bill 072X claim line | Drug given for a condition unrelated to ESRD |
| DME supplier | DMEPOS claim line | Supply used for a non-renal purpose |
| Pharmacy or other Part B supplier | Part B claim line | Drug furnished for a separate condition |
Services Unrelated to ESRD Treatment
The clinical reason for the service decides AY eligibility. A test that monitors dialysis adequacy is ESRD-related, even when another diagnosis appears on the order. A test ordered to stage a tumor is unrelated, because it serves the cancer care plan.
In practice, coders should read the order and the progress note together. The ordering provider’s documented reason carries more weight than the diagnosis list on the claim. When the purpose is unclear, a provider query is safer than a guess. Coders should also report the correct ESRD ICD-10 codes alongside the separate diagnosis.
Laboratory Services for Other Medical Conditions
Lab tests are the most common AY scenario in ESRD billing. CMS gives a direct example: an ESRD patient with cancer has a lab test related to cancer treatment. The lab should submit that claim with AY to receive separate payment.
CMS updates the consolidated billing lab list every year. Noridian notes the list is not all-inclusive. Any lab ordered for ESRD treatment stays in the bundle, whether or not its code appears on the list.
Emergency Department Exception: Since January 1, 2012, hospitals do not need AY on lab tests billed with an ER visit. CMS accepted that ED physicians often cannot know whether a test relates to ESRD at ordering. Noridian adds that facilities should not send patients to the ER for routine dialysis labs.
Drugs and Biologicals Unrelated to ESRD
AY can support separate payment for a drug given for a non-ESRD reason, with one major exception. CMS designates certain functional drug categories as always ESRD-related. Drugs in these categories are never paid separately to ESRD facilities, with or without AY. CMS transmittals have applied this rule to:
- Anemia management drugs, including ferric carboxymaltose
- Bone and mineral metabolism drugs, including oral cinacalcet (J0604)
- Antipruritic drugs used for dialysis patients, including difelikefalin (J0879)
Drugs outside those categories follow a case-by-case review. An antibiotic for community-acquired pneumonia may qualify for AY when the record shows that purpose. An antibiotic for a dialysis catheter infection does not, because access-related infections are part of ESRD care.
Services Furnished by an ESRD Facility
An ESRD facility must add AY to a non-ESRD service line to receive payment outside the ESRD PPS. Noridian JE Part A guidance states this directly. Without AY, Medicare treats labs and drugs on the facility claim as part of the bundle.
Facilities bill on type of bill 072X with line-level modifiers. AY belongs on the specific line for the unrelated item, not on every line of the claim. Other required ESRD modifiers, such as vascular access and URR modifiers, still apply on their own lines.
When Should You NOT Use the AY Modifier?
Do not use AY for any service tied to ESRD treatment or already included in the ESRD payment bundle. The modifier is a statement of clinical fact on a federal claim. Using it without support turns a routine claim into a compliance risk. Avoid AY in these situations:
- Labs ordered to monitor dialysis, anemia, or bone mineral status
- Drugs in a functional category CMS treats as always ESRD-related
- Services that fail coverage, frequency, or medical necessity requirements
- Orders listing a separate diagnosis while the real purpose is dialysis care
- Any claim where AY is added only to get past a consolidated billing edit
Warning: Do not append AY just because the patient has another diagnosis. The documented clinical purpose and the applicable billing rules must both support its use. AY cannot override a consolidated billing exclusion or guarantee reimbursement.
Federal auditors do check this. An HHS Office of Inspector General (OIG) review of DaVita Laboratory Services found improper AY claims. Some were for tests furnished to treat ESRD. The OIG identified $469,008 in payments for tests billed with AY or not ordered by a physician.
How to Bill the AY Modifier Correctly
Correct AY billing follows a fixed sequence from service review to payment tracking. Most AY denials trace back to a skipped step, usually the clinical purpose check. Use this seven-step workflow for every line where AY might apply:
| Step | What to Do | What to Verify |
|---|---|---|
| 1. Identify the Service | Confirm the CPT or HCPCS code, drug, item, or lab test | Code is valid for the date of service |
| 2. Establish the Clinical Purpose | Read the order, diagnosis, and medical record together | The documented reason is unrelated to ESRD treatment |
| 3. Check Consolidated Billing Rules | Compare the code to the current CMS consolidated billing list | Whether the service is bundled, excluded, or always ESRD-related |
| 4. Review Coding Instructions | Check the Medicare Claims Processing Manual, Chapter 8, and MAC guidance | Claim-type and code-specific requirements |
| 5. Append AY When Supported | Report AY on the specific claim line for the unrelated service | Modifier position and other required modifiers |
| 6. Validate and Submit | Scrub diagnosis codes, units, documentation, and modifiers | Diagnosis pointer links to the non-ESRD condition |
| 7. Track Adjudication | Review remittance advice, rejections, and denials | Correct and resubmit, or appeal when appropriate |
Step 2 takes the most time, and it protects the claim most. Teams handling nephrology medical billing often build a short purpose field into their charge capture form. That one field gives coders the reason without searching the full note.
Missing AY on a bundled service billed by a non-facility provider usually means a denied line. Older CMS instructions tied these lines to claim adjustment reason code (CARC) 109. Always confirm current remark codes in your MAC’s remittance guidance.
AY Modifier Billing Examples
The scenarios below show how billing teams apply the purpose test in daily work. These are illustrative scenarios, not blanket coding determinations. Each claim still needs its own documentation review.
| Scenario | AY Decision | Billing Consideration |
|---|---|---|
| Lab test for an unrelated cancer workup | AY supported | CMS uses this exact example; confirm the order documents the cancer purpose |
| Monthly lab panel for routine ESRD management | No AY | Test is related to ESRD treatment and stays in the bundle |
| Antibiotic for community-acquired pneumonia | AY possible | Verify drug-specific rules and documentation before reporting |
| Antibiotic for a dialysis catheter infection | No AY | Vascular access infections are part of ESRD care |
| Oral cinacalcet for bone and mineral metabolism | No AY | Always ESRD-related; no separate payment with or without AY |
| Lab test during an emergency department visit | AY not required | ED lab exception applies since January 1, 2012 |
| Separate diagnosis, but the service supports dialysis care | No AY | A separate diagnosis alone does not establish an unrelated purpose |
Common AY Modifier Billing Errors
Most AY errors come from skipping the purpose review or misreading what the modifier does. Each error below has a practical correction your team can build into claim review:
| Error | Why It Happens | Practical Correction |
|---|---|---|
| Applying AY without reviewing the service’s link to ESRD | Coders rely on the diagnosis list alone | Require the documented order purpose before any AY append |
| Assuming AY guarantees separate payment | The modifier is treated as a payment switch | Check coverage, medical necessity, and drug category rules first |
| Ignoring consolidated billing requirements | Teams use outdated code lists | Load the current-year CMS consolidated billing list each January |
| Weak diagnosis or documentation support | Orders lack a stated reason | Query the ordering provider before the claim goes out |
| Placing AY on the wrong claim line | Modifiers applied at claim level by templates | Audit charge templates so AY attaches only to the unrelated line |
| Missing current code-specific or payer rules | MAC updates are not tracked | Assign one person to review MAC and MLN updates monthly |
Errors built into templates deserve extra attention. An automated rule that appends AY to every lab for ESRD patients will produce improper claims at scale. Review these rules at least once a year, and after every consolidated billing update.
Documentation and Compliance Checklist
Run this checklist on every claim line where AY may apply. It works as a pre-submission review for coders and a spot-audit tool for billing managers:
- The medical record supports the service’s clinical purpose.
- Documentation explains why the service is unrelated to ESRD treatment.
- The diagnosis code and billed service are clinically consistent.
- Current CMS consolidated billing rules have been reviewed.
- Code-specific and payer requirements have been verified.
- AY is reported on the correct claim line when applicable.
- Claim edits and remittance advice have been reviewed after adjudication.
This checklist supports claim review, but it does not replace official billing instructions. Always confirm details against current CMS manuals and your MAC’s published guidance. Strong medical coding and billing accuracy depends on both the rule and the record.
AY vs. AX Modifier: What Changed in 2026?
AY and AX are different modifiers, and CMS ended routine AX reporting for ESRD claims in 2026. AX means “item furnished in conjunction with dialysis services.” ESRD facilities historically used it to trigger add-on payments, including TDAPA, TPNIES, and CRA TPNIES.
Under Change Request 14354, CMS stopped using AX in ESRD payment calculations. The policy took effect July 1, 2026, and CMS systems applied it from July 6, 2026. The updated transmittal R13740CP was issued on April 17, 2026.
| Attribute | AY Modifier | AX Modifier |
|---|---|---|
| Descriptor | Item or service furnished to an ESRD patient that is not for ESRD treatment | Item furnished in conjunction with dialysis services |
| Historical Purpose | Requests separate payment for unrelated services | Flagged items eligible for TDAPA, TPNIES, and CRA TPNIES add-ons |
| Who Reports It | ESRD facilities, labs, DME suppliers, other providers | ESRD facilities |
| Status for Dates of Service on or After July 1, 2026 | Still active | Do not report on renal dialysis services unless CMS instructs otherwise |
| Payment Effect | Allows separate payment when the service is otherwise eligible | No longer used in ESRD payment calculations |
The two modifiers are not interchangeable. Facilities should remove AX from charge templates and billing macros for dates of service on or after July 1, 2026. Per MLN Matters MM14354, other TDAPA and TPNIES billing guidance remains in place. This update is one of several recent ESRD payment changes affecting dialysis claims.
Frequently Asked Questions About the AY Modifier
What Does the AY Modifier Mean in Medicare Billing?
AY means an item or service was furnished to an ESRD patient but was not for ESRD treatment. Medicare uses it to separate unrelated services from the ESRD PPS bundle. Labs, ESRD facilities, DME suppliers, and other providers report it at the claim line level. Commercial payers may follow their own rules.
When Is the AY Modifier Required for ESRD Patients?
AY is required when a bundled-type service is furnished to an ESRD patient for a non-ESRD reason. The billing provider needs it to request payment outside the ESRD PPS. Without it, Medicare treats the service as part of the facility bundle. Emergency department lab tests are the main exception.
Can the AY Modifier Be Used for Unrelated Laboratory Tests?
Yes, AY applies to lab tests ordered for a condition other than ESRD. CMS cites a cancer-related test for an ESRD patient as a direct example. The order must document the unrelated purpose. Labs ordered to manage ESRD stay in the bundle, even when the patient has other diagnoses.
Does the AY Modifier Guarantee Separate Payment?
No, AY only identifies a service as unrelated to ESRD treatment. The service must still meet coverage, medical necessity, and coding rules. Drugs in ESRD-related categories, such as anemia management, receive no separate payment with or without AY. The claim must stand on its own merits.
Can an ESRD Facility Bill Unrelated Services Separately?
Yes, an ESRD facility can bill unrelated services separately with AY on the claim line. Facilities report these lines on type of bill 072X. Without AY, Medicare treats facility labs and drugs as bundled. Drugs CMS classifies as always ESRD-related remain unpayable outside the bundle.
What Documentation Supports the AY Modifier?
The order and medical record must show the service treats a condition other than ESRD. Useful records include an order with a stated reason and a note describing the separate condition. A matching diagnosis code completes the support. The diagnosis pointer on the claim should link to that non-ESRD condition.
What Is the Difference Between the AY and AX Modifiers?
AY marks a service as unrelated to ESRD, while AX marked items furnished with dialysis. AX historically triggered TDAPA and TPNIES add-on payments. For dates of service on or after July 1, 2026, CMS instructs facilities not to report AX unless told otherwise. AY remains active and unchanged.
How Do You Choose the Best Nephrology Medical Billing Service?
Choose a nephrology billing service with proven ESRD experience, current CMS knowledge, and clear denial reporting. The right partner should understand consolidated billing, AY and AX rules, and monthly capitation codes. Ask how the team tracks MAC updates and audits modifier use. For a side-by-side comparison, see our list of the best nephrology medical billing companies in the USA.
