In simple words: This code covers the time an ambulance waits for a patient, billed in half-hour blocks.

This code represents the time an advanced life support (ALS) or basic life support (BLS) ambulance waits, reportable in one-half-hour increments. Ambulance waiting time is the time spent by an ambulance service provider waiting for a patient. This typically includes the time the ambulance waits while a patient is having a procedure, test, or service, or the time taken to transfer a patient from the ambulance attendants to the facility’s emergency department.

Example 1: A patient requires an ALS ambulance to transport them to a hospital for an emergency condition. The ambulance arrives at the scene, but the patient needs 45 minutes for on-scene stabilization before transport. One unit of A0420 would be billed., A patient receiving dialysis requires a BLS ambulance for transport back home. After the dialysis session, the patient requires a 1-hour wait for the prescribed medication. Two units of A0420 would be billed., An ALS ambulance transports a patient to a hospital's emergency department. Upon arrival, the hospital staff are occupied with another emergency, and the ambulance team has to wait 30 minutes to transfer the patient's care. One unit of A0420 is billable for this waiting period.

Documentation should clearly indicate the type of ambulance service (ALS or BLS), the arrival time at the scene, the time the wait began, the reason for the wait, and the duration of the wait. Any specific circumstances justifying the wait should also be noted.