The CMS Level field is specifically for Medicare Transports.  It has been used though by various insurance companies to determine what level of care was provided.  Here are the definitions for each level as determined by the U.S. Govt.

Basic Life Support (BLS) – Includes the provision of medically necessary supplies and services and BLS ambulance transports defined by the State where you provide the transport. An emergency response is one that, at the time you are called, you respond immediately. A BLS emergency is an immediate emergency response in which you begin as quickly as possible to take the steps necessary to respond to the call.

Advanced Life Support, Level 1 (ALS1) – Includes the provision of medically necessary supplies and services and the provision of an ALS assessment or at least one ALS intervention. An ALS assessment is performed by an ALS crew as part of an emergency response that is necessary because the beneficiary’s reported condition at the time of dispatch indicates only an ALS crew is qualified to perform the assessment. An ALS assessment does not necessarily result in a determination that the beneficiary requires an ALS level of transport. In the case of an appropriately dispatched ALS emergency service, if the ALS crew completes an ALS assessment, the services provided by the ambulance transportation service provider or supplier shall be covered at the ALS emergency level. This is regardless of whether the beneficiary required ALS intervention services during the transport, provided the ambulance transportation itself was medically reasonable and necessary and all other coverage requirements are met. An ALS intervention is a procedure that must be performed by an emergency medical technician-intermediate (EMT-Intermediate) or an EMT-Paramedic in accordance with State and local laws. An ALS1 emergency is an immediate emergency response in which you begin as quickly as possible to take the steps necessary to respond to the call.

Advanced Life Support, Level 2 (ALS2) – Includes the provision of medically necessary supplies and services, involving:

At least three separate administrations of one or more medications by intravenous push/bolus or by continuous infusion(excluding crystalloid fluids) or 

At least one of these ALS2 procedures: Manual defibrillation/cardioversionEndotracheal intubation Central venous line Cardiac pacing Chest decompression Surgical airway Intraosseous line

Specialty Care Transport (SCT) – Includes the provision of medically necessary supplies and services at a level of service beyond the scope of an EMT-Paramedic. SCT is the interfacility transportation of a critically ill or injured beneficiary that is necessary because the beneficiary’s condition requires ongoing care furnished by one or more professionals in an appropriate specialty (such as emergency or critical care nursing, emergency medicine, respiratory or cardiovascular care, or an EMT-paramedic with additional training).

Paramedic Intercept (PI) – When an entity that does not provide the ambulance transport provides ALS services. PI may be required when you can provide only a BLS level of service and the beneficiary requires an ALS level of service (such as electrocardiogram monitoring, chest decompression, or intravenous therapy). Certain additional requirements apply that, as of the publication of this booklet, are met only by certain entities operating in some western counties of New York State.