Medicare requires ambulance suppliers to report two-character origin and destination modifiers on most ambulance transportation claims. These modifiers identify where the patient was picked up and where the patient was transported.
The letter I represents a Site of Transfer, such as an airport, helicopter landing zone, helipad, or other transfer point where the patient is transferred between different modes of ambulance transportation. It is not a standalone modifier and must always be paired with another origin or destination code.
Modifier I is commonly used when a patient is transferred between ground ambulance and air ambulance to ensure rapid transport for time-sensitive medical emergencies.
Modifier
I
Modifier Name
Site of Transfer (Airport or Helicopter Pad) Between Modes of Ambulance Transport
Plain English Explanation
The letter I tells Medicare:
“The ambulance transport either started from or ended at a transfer site where the patient changed from one type of ambulance transportation to another.”
Purpose of Modifier I
Modifier I is used to:
- Identify transfer locations between ambulance transportation modes.
- Distinguish transfer sites from hospitals, residences, and other facilities.
- Support accurate Medicare ambulance billing.
- Identify multimodal ambulance transports.
- Ensure compliance with CMS origin and destination reporting requirements.
Understanding Modifier I
Ambulance origin/destination modifiers always consist of two letters.
- The first letter identifies the origin (pickup location).
- The second letter identifies the destination (drop-off location).
The letter I may appear in either position.
Common Modifier Combinations
| Modifier | Meaning |
|---|---|
| HI | Hospital → Transfer Site |
| IH | Transfer Site → Hospital |
| RI | Residence → Transfer Site |
| IR | Transfer Site → Residence |
| SI | Scene of Accident → Transfer Site |
| IS | Transfer Site → Scene of Accident (rare) |
| NI | Skilled Nursing Facility → Transfer Site |
| IN | Transfer Site → Skilled Nursing Facility |
What Is a Transfer Site?
Examples include:
- Airport used for air ambulance transfers
- Hospital helipad
- Community helicopter landing zone
- Fixed-wing aircraft transfer location
- Designated ambulance exchange point
- Other approved transfer locations where the patient changes from one ambulance mode to another
When to Use Modifier I
Use Modifier I when:
- The patient is transferred between ground and air ambulance.
- The pickup or destination is an approved transfer site.
- The transfer is medically necessary.
- Medicare ambulance coverage requirements are satisfied.
When NOT to Use Modifier I
Do not use Modifier I when:
- The patient is transported directly between two facilities without changing transportation modes.
- The location is a hospital (H), residence (R), physician’s office (P), or skilled nursing facility (N).
- Modifier I is reported by itself.
- No transfer between ambulance transportation modes occurs.
Medicare Rules
Under Medicare:
- Modifier I must always be reported as part of a valid two-letter origin/destination modifier.
- It identifies only the transfer point between transportation modes.
- The ambulance run report must clearly document the transfer.
- Medical necessity must support both ambulance transports when separate claims are submitted.
- Incorrect origin/destination coding may result in claim rejection or denial.
Always follow the current CMS Medicare Claims Processing Manual and Medicare Administrative Contractor (MAC) guidance.
Commercial Insurance Rules
Many commercial insurers recognize Medicare’s ambulance origin/destination coding system.
However, they may have different requirements regarding:
- Air ambulance coverage.
- Prior authorization.
- Transfer documentation.
- Medical necessity.
- Reimbursement methodology.
Always verify payer-specific policies before claim submission.
Documentation Requirements
Documentation should include:
- Pickup location.
- Destination location.
- Transfer site name and address.
- Ambulance run report.
- Air ambulance documentation (if applicable).
- Medical necessity.
- Date and time of transfer.
- Mileage documentation.
- Crew signatures.
- Receiving provider documentation.
Real Billing Examples
Example 1 – Hospital to Helipad
A critically injured patient is transported by ground ambulance from a community hospital to the hospital helipad for transfer to an air ambulance.
Billing
- HCPCS A0428 or A0429, as appropriate
- Modifier HI
Example 2 – Helipad to Trauma Center
An air ambulance delivers the patient to a regional trauma center. A ground ambulance transports the patient from the helipad to the hospital emergency department.
Billing
- HCPCS A0428
- Modifier IH
Example 3 – Residence to Airport Transfer Site
A patient is transported by ground ambulance from home to an airport for transfer to a fixed-wing air ambulance.
Billing
- HCPCS A0428
- Modifier RI
Example 4 – Incorrect Use
A patient is transported directly from home to the hospital without any transfer between ambulance transportation modes.
Reporting Modifier I is incorrect because no transfer site was involved.
CMS-1500 Claim Example
| Field | Example |
| HCPCS | A0428 |
| Modifier | HI |
| Diagnosis Pointer | Appropriate ICD-10-CM diagnosis |
| Mileage | A0425 (if applicable) |
Common Denial Reasons
- Modifier I billed alone.
- No documented transfer between ambulance modes.
- Incorrect origin/destination combination.
- Missing air ambulance documentation.
- Medical necessity not supported.
- Missing mileage documentation.
- Incomplete ambulance run report.
How to Correct the Denial
- Review the ambulance run report.
- Verify that a transfer between ambulance modes occurred.
- Confirm the transfer site location.
- Correct the two-letter modifier if needed.
- Submit supporting documentation.
- Appeal when appropriate.
Coding Tips
- Never report Modifier I alone.
- Confirm that the patient changed between ambulance transportation modes.
- Document the transfer site clearly.
- Coordinate documentation between ground and air ambulance providers.
- Review CMS origin/destination coding tables regularly.
Modifier I vs Modifier H
| Modifier | Description |
| I | Transfer Site Between Ambulance Modes |
| H | Hospital |
Modifier I vs Modifier R
| Modifier | Description |
| I | Transfer Site |
| R | Residence |
Modifier I vs Modifier S
| Modifier | Description |
| I | Transfer Site |
| S | Scene of Accident or Acute Event |
Frequently Asked Questions (FAQs)
Q1. Can Modifier I be billed by itself?
Answer: No. Modifier I must always be paired with another valid ambulance origin/destination code.
Q2. What does Modifier I represent?
Answer: A transfer site, such as an airport or helicopter pad, where a patient changes between ambulance transportation modes.
Q3. What does HI mean?
Answer: Hospital → Transfer Site.
Q4. When is Modifier I commonly used?
Answer: During transfers between ground ambulance and air ambulance services.
AR Caller Tips
When following up on ambulance denials:
- Verify that the transfer site is documented.
- Confirm a change between transportation modes occurred.
- Review both ground and air ambulance records.
- Verify medical necessity.
- Ensure the correct two-letter modifier was reported.
- Document the payer representative’s name, reference number, and appeal instructions.
Interview Questions
Question 1
What does Modifier I represent?
Answer: A transfer site between different modes of ambulance transportation.
Question 2
Can Modifier I be billed alone?
Answer: No. It must always be combined with another valid ambulance origin/destination code.
Question 3
Give an example of a valid Modifier I combination.
Answer: HI (Hospital → Transfer Site) or IH (Transfer Site → Hospital).
Practice Scenario
Scenario
A patient is transported by ground ambulance from a community hospital to a helicopter landing zone, where an air ambulance takes over for transport to a tertiary care center.
Question
Which modifier should be reported on the ground ambulance claim?
Answer
The correct modifier is HI, indicating Hospital → Transfer Site.
Related Ambulance Modifiers
- D – Diagnostic or Therapeutic Site
- E – Residential, Domiciliary, or Custodial Facility
- G – Hospital-Based ESRD Facility
- H – Hospital
- J – Freestanding ESRD Facility
- N – Skilled Nursing Facility
- P – Physician’s Office
- R – Residence
- S – Scene of Accident or Acute Event
- X – Intermediate Stop at Physician’s Office (Destination Only)
Common Billing Mistakes
- Reporting Modifier I as a standalone modifier.
- Using Modifier I when no transfer between ambulance modes occurred.
- Reporting the wrong origin/destination sequence.
- Missing transfer site documentation.
- Missing air ambulance coordination records.
- Incomplete mileage documentation.
Key Takeaways
- I represents a Site of Transfer between ambulance transportation modes.
- It is not a standalone modifier.
- It must always be reported with another valid ambulance origin/destination code.
- It is commonly used for ground-to-air or air-to-ground ambulance transfers.
- Accurate documentation of the transfer site and medical necessity is essential for Medicare reimbursement.
References
- CMS Medicare Claims Processing Manual, Chapter 15 – Ambulance Services.
- CMS Ambulance Origin and Destination Codes Guidance.
- Medicare Administrative Contractor (MAC) Ambulance Billing Guidance.
- HCPCS Level II Code Book.
Conclusion
The I ambulance origin/destination code identifies transports involving a transfer site where patients change between ambulance transportation modes, such as ground-to-air or air-to-ground transfers. Proper reporting requires pairing I with another valid location code, maintaining complete documentation, and complying with CMS ambulance billing requirements. Accurate use helps ensure compliant billing, timely reimbursement, and reduced claim denials.
Educational Disclaimer
This article was prepared with the assistance of artificial intelligence (AI) for educational and informational purposes. It is based on publicly available CMS guidance, Medicare ambulance billing principles, and general medical coding practices. It is not an official publication of CMS or the American Medical Association (AMA). Always consult the latest CMS Medicare Claims Processing Manual, the HCPCS Level II codebook, Medicare Administrative Contractor (MAC) guidance, and payer-specific billing policies before coding, billing, or submitting claims.