Quick answer: Every ambulance claim line carries a two-letter modifier that shows where the transport started and where it ended. The first letter is the origin and the second is the destination, so SH means scene of an accident or acute event to hospital, RH means residence to hospital, and HH means hospital to hospital. Medicare requires the modifier on each ambulance HCPCS line, including the mileage line, and a missing, reversed or mismatched modifier is a common reason an ambulance claim is rejected or denied.
Modifiers are a small part of ambulance medical billing, but they decide whether a payer can match the transport to a covered destination. For an overview of the whole process, see what is ambulance medical billing. This guide lists all 11 location codes, explains the combinations EMS billers use most, and covers the QM, QN, GM and QL modifiers that sit alongside them.
How ambulance modifiers are built
An ambulance modifier is made by joining two single-letter location codes. The first position is the pickup location and the second position is the drop-off location. Medicare’s rules are set out in the Medicare Claims Processing Manual, Chapter 15, Section 30, and Medicare Administrative Contractors such as Noridian, First Coast and Palmetto GBA publish the same list.
Three rules apply to every claim:
- Report the modifier on each ambulance HCPCS line: the base rate code (for example A0427 or A0429) and the mileage code (A0425 for ground transports).
- Use the same origin and destination on the base rate and mileage lines for the same trip.
- The letter X can only be used in the second position. It is never an origin.
For the base codes and mileage rules these modifiers attach to, see our ambulance billing codes guide.
The 11 ambulance origin and destination codes
| Code | Location | Examples and notes |
|---|---|---|
| D | Diagnostic or therapeutic site other than P or H, when P or H are used as origin codes | Freestanding imaging center, radiation therapy center |
| E | Residential, domiciliary or custodial facility (other than a skilled nursing facility) | Assisted living facility, group home |
| G | Hospital-based ESRD facility | Dialysis unit operated by a hospital |
| H | Hospital | Includes the emergency department |
| I | Site of transfer between modes of ambulance transport | Airport or helicopter pad where a ground crew hands off to an air crew |
| J | Freestanding ESRD facility | Dialysis center not operated by a hospital |
| N | Skilled nursing facility | Medicare-certified SNF |
| P | Physician’s office | Use P, not D, when a physician’s office is the destination |
| R | Residence | The patient’s home, including emergency pickups at home |
| S | Scene of accident or acute event | Roadside, workplace, public place |
| X | Intermediate stop at a physician’s office on the way to the hospital | Destination position only |
HH modifier for ambulance: hospital to hospital
The HH modifier means the patient was picked up at a hospital and delivered to another hospital. It is the standard modifier for interfacility transfers, such as moving a patient from a community hospital emergency department to a hospital with a cardiac catheterization lab, trauma center or burn unit.
Medicare generally covers a hospital-to-hospital transfer when the patient needs care that the first hospital cannot provide and the receiving hospital is the nearest one that can provide it. Your documentation should show both points: why the patient could not be treated at the sending hospital, and why the destination was chosen.
When HH is billed incorrectly
- The patient was discharged home. A hospital discharge to the patient’s home is HR, not HH.
- The patient remained an inpatient of the sending hospital and was taken to another facility for a test or treatment, then returned. That round trip is generally part of the inpatient stay and is paid by the sending hospital under an arrangement, not billed separately to Medicare Part B.
- The record does not explain why the destination was needed. For non-emergency transfers, a missing or incomplete physician certification statement (PCS) leads to denials.
Our interfacility transport billing guide covers transfer billing, bundling and PCS rules in more depth.
SH modifier for ambulance: scene to hospital
The SH modifier means the patient was picked up at the scene of an accident or acute event and taken to a hospital. It is typical for 911 responses on a roadway, at a workplace or in a public place, and it is usually paired with an emergency level of service such as A0427 (ALS1 emergency) or A0429 (BLS emergency), plus A0425 for mileage.
The most frequent SH mistake is using S for a 911 call to the patient’s home. A home is a residence, so the origin code is R and the modifier is RH, even when the call is an emergency.
RH modifier: residence to hospital
The RH modifier means the patient was picked up at home and taken to a hospital. It covers both emergency calls to a residence and scheduled non-emergency trips. For scheduled non-emergency trips, payers look closely at medical necessity, so the patient care report should state why the patient could not travel by other means, for example being bed-confined.
Medicare’s coverage tests, PCS requirements and signature rules for these trips are covered in our Medicare ambulance billing guide.
Common ambulance modifier combinations
| Modifier | Trip | Typical use |
|---|---|---|
| SH | Scene to hospital | 911 response to a roadway, workplace or public place |
| RH | Residence to hospital | Emergency call at home or scheduled admission |
| HH | Hospital to hospital | Interfacility transfer for a higher level of care |
| HN | Hospital to skilled nursing facility | Discharge to a SNF |
| NH | Skilled nursing facility to hospital | SNF resident sent to the emergency department |
| HR | Hospital to residence | Discharge home when ambulance transport is medically necessary |
| EH | Residential facility to hospital | Assisted living resident transported to hospital |
| RJ and JR | Residence to freestanding dialysis, and the return trip | Repetitive scheduled dialysis transports |
| RG and GR | Residence to hospital-based dialysis, and the return trip | Dialysis at a hospital-operated unit |
| SI and IH | Scene to helicopter pad, then pad to hospital | Ground crew hands off to an air ambulance |
Repetitive scheduled transports to dialysis receive extra review from Medicare contractors, so confirm the PCS and any prior authorization rules in your jurisdiction before billing RJ or RG trips.
QM and QN modifiers
QM and QN are not location codes. Institutional providers, such as hospital-based ambulance services billing on an institutional claim, must add one of them to each ambulance HCPCS line in addition to the origin and destination modifier:
- QM: ambulance service provided under arrangement by a provider of services.
- QN: ambulance service furnished directly by a provider of services.
Independent ambulance companies billing as suppliers do not use QM or QN. Contractor guidance states that institutional ambulance lines missing QM or QN will be denied.
Other ambulance modifiers to know
| Modifier | Meaning |
|---|---|
| GM | Multiple patients on one ambulance trip, reported on each line in addition to the origin and destination modifier |
| QL | Patient pronounced dead after the ambulance was called |
| TQ | BLS transport by a volunteer ambulance provider; not payable by Medicare |
| GY | Service is statutorily excluded or does not meet the definition of a Medicare benefit |
Five modifier errors that cause ambulance denials
- Modifier on the base line but not the mileage line. Both lines need the same origin and destination.
- Reversed letters. HR (hospital to residence) and RH (residence to hospital) describe opposite trips with different coverage questions.
- D used for a physician’s office. Palmetto GBA has reminded providers to use P when the destination is a physician’s office.
- S used for home pickups. An emergency at the patient’s home is RH, not SH.
- Missing QM or QN on institutional claims, or HH billed to Part B for inpatient round trips that belong to the sending hospital.
How to keep modifiers accurate
- Take origin and destination from the location fields in the ePCR, not from dispatch notes, and confirm them against the pickup and drop-off addresses.
- Add a claim scrubber edit that rejects any ambulance base or mileage line without a valid two-letter modifier, and any modifier with X in the first position.
- Check a sample of claims each month for modifiers that do not match the narrative, such as an SH trip that started at a home address.
Our ambulance coding services check level of service, origin and destination modifiers and loaded mileage before each claim is submitted. If you want to see how your modifiers hold up, request a free billing audit and we will review coding accuracy on a sample of your claims.
Frequently asked questions
What does the HH modifier mean on an ambulance claim?
HH means the transport started at a hospital and ended at another hospital. It is used for interfacility transfers, and Medicare generally covers them when the receiving hospital is the nearest one able to provide care the first hospital could not.
What is the SH modifier for ambulance?
SH means the patient was picked up at the scene of an accident or acute event and taken to a hospital. It is common on 911 claims. A 911 call to the patient’s home uses RH instead.
What does the RH modifier mean?
RH means residence to hospital. It applies to both emergency calls at the patient’s home and scheduled non-emergency trips from home to a hospital.
What is the difference between QM and QN?
Both are used only by institutional providers. QM means the ambulance service was provided under arrangement, and QN means the provider furnished it directly. One of them goes on each ambulance HCPCS line alongside the origin and destination modifier.
Do Medicaid and commercial payers require origin and destination modifiers?
Many follow Medicare’s modifier list. For example, UnitedHealthcare’s hospital-based ambulance policy denies transports reported without a valid two-letter ambulance modifier. Check each payer’s manual, because some state Medicaid programs add their own requirements.
Can X be used as an origin code?
No. X means an intermediate stop at a physician’s office on the way to a hospital and can only appear in the second (destination) position.
Sources
- Noridian JF Part A: Modifiers
- First Coast Service Options: Ambulance modifiers
- Palmetto GBA JM: Origin/Destination Ambulance Modifiers
- UnitedHealthcare: Hospital Based Ambulance Policy
- Medicare Claims Processing Manual, Chapter 15, Section 30
- Medicare Benefit Policy Manual, Chapter 10