By Ryan Smith • Updated: September 2026 • 8 Min Read
Quick answer: Every ground ambulance claim pairs a level-of-service HCPCS code (BLS, ALS1, ALS2, or SCT) with a two-letter origin and destination modifier. The level code must match the care documented on the run report, and the modifier must match where the patient was picked up and dropped off. Both must be right for the claim to pay correctly.
Modifier errors are one of the most common and most preventable reasons ambulance claims are denied or underpaid. This guide explains each level of service, how origin and destination modifiers work, how the two combine on real transports, and where agencies most often go wrong.
The ground ambulance level-of-service codes
- A0428, BLS non-emergency and A0429, BLS emergency: Basic life support, used when the transport required only basic care and monitoring with no ALS assessment or intervention.
- A0426, ALS1 non-emergency and A0427, ALS1 emergency: Advanced life support, level 1. Supported by at least one ALS intervention, or, for emergency responses, by an ALS assessment performed by ALS personnel when the dispatch information indicated the patient needed an ALS-level response.
- A0433, ALS2: Requires either at least three separate administrations of one or more medications by intravenous push, bolus, or continuous infusion (excluding crystalloid, hypotonic, isotonic, and hypertonic solutions), or at least one specific procedure such as manual defibrillation or cardioversion, endotracheal intubation, central venous line placement, cardiac pacing, chest decompression, surgical airway, or intraosseous line.
- A0434, SCT (specialty care transport): An interfacility transport of a critically ill or injured patient who needs ongoing care beyond the scope of a paramedic, provided by one or more health professionals in an appropriate specialty area such as nursing, emergency medicine, respiratory care, or cardiovascular care.
- A0425, ground mileage: Billed separately for loaded miles only.
How origin and destination modifiers work
The origin and destination modifier is two letters: the first shows where the patient was picked up, and the second shows where the patient was dropped off. Common letters include:
- R: residence
- H: hospital
- N: skilled nursing facility
- E: residential, domiciliary, or custodial facility other than a skilled nursing facility
- S: scene of an accident or acute event
- P: physician’s office
- D: diagnostic or therapeutic site other than P or H
- G and J: hospital-based and freestanding dialysis facilities
- I: site of transfer between modes of ambulance transport, such as a helipad
So RH means residence to hospital, SH means scene to hospital, and HN means hospital to skilled nursing facility. Hospital-based ambulance providers may also need QM or QN modifiers to show whether the service was provided under arrangement or directly.
How the pieces combine: three examples
- 911 call, IV medication given, taken from home to the emergency department: ALS1 emergency (A0427) with modifier RH, plus loaded mileage. The run report must document the ALS intervention.
- Cardiac arrest at a workplace, three IV doses of epinephrine, taken to the hospital: ALS2 (A0433) with modifier SH, supported by documentation of each medication administration with times.
- Ventilated patient transferred between hospitals with a critical care nurse managing infusions: SCT (A0434) with modifier HH, only if the documentation shows the patient’s condition required care beyond the paramedic scope.
Where agencies most often get this wrong
- Coding ALS based on the crew’s certification level rather than the care actually documented for that transport
- Under-documenting the ALS assessment, so an emergency ALS1 claim is not supported even when an ALS-level response was appropriate
- Treating every interfacility transfer as SCT without confirming the patient needed specialty-level care
- Using the wrong origin letter for facility pickups, such as coding an assisted living facility as a skilled nursing facility
- Counting medications that do not qualify toward the ALS2 threshold, such as IV fluids
The fix starts with documentation, not coding
A coder can only bill what the run report supports. The most reliable way to get modifier combinations right is training crews to document the specific findings and interventions that justify the level of service on every call, not only on complex ones. Our ambulance coding service reviews each run report against these rules before submission, and our guide to building a compliant documentation workflow shows how to build these habits into crew training. Modifier errors also appear on our list of the seven most common ambulance billing denials.
Frequently asked questions
What is the difference between ALS1 and ALS2?
ALS1 requires at least one ALS intervention, or an ALS assessment on an emergency response. ALS2 requires at least three separate administrations of qualifying IV medications, or at least one listed advanced procedure such as intubation, manual defibrillation, cardiac pacing, or an intraosseous line.
What does the RH modifier mean on an ambulance claim?
RH means the patient was picked up at a residence (R) and taken to a hospital (H). The first letter of the modifier always shows the origin and the second letter shows the destination.
Can you bill ALS if a paramedic was on board but only provided basic care?
Generally, no. The level of service is based on the care provided and documented, not on the crew’s certification. On emergency responses, an ALS assessment by ALS personnel can support ALS1 when dispatch information indicated an ALS-level need, but it must be documented.
When does an interfacility transfer qualify as SCT?
Only when a critically ill or injured patient needs ongoing care beyond the paramedic scope, provided by health professionals in an appropriate specialty area. A routine transfer with a paramedic crew does not qualify, even between two hospitals.
Not sure your current modifier usage matches what your documentation supports? Get a free billing audit and we’ll review a sample of your recent claims with you.