A0999: The unlisted ambulance code and how some Medicaid programs use it for rides

What A0999 is

A0999 is the catch-all ambulance code. Its HCPCS description is simply “Unlisted ambulance service.” It is meant for an ambulance service that no existing code describes, and CMS includes it on its October 2026 list of not otherwise classified codes. The HCPCS entry explains how that range fits in the wider code set.

Medicare gives the code no national price. The October 2026 HCPCS file assigns pricing indicator 57, “other carrier priced,” and coverage code D, “special coverage instructions apply.” Compare A0428, the non-emergency basic life support base rate, which carries a fixed rate on the Florida, Arkansas and Mississippi Medicaid schedules.

How payers price and review it

An unlisted code gets read by a person, not paid by a rate table. CMS’s HCPCS coding procedures say claims with miscellaneous codes are manually reviewed, that the item or service must be clearly described, and that pricing information and documentation of need must come with it. The same guidance tells billers to check with the payer first in case a specific code fits better.

That review shapes the claim:

1. Describe the service on the line. When a payer asks for a narrative, the NUCC manual (version 13.0, July 2025) puts the description of an unspecified code in the shaded part of item 24, after the qualifier ZZ.
2. Send the documents the payer names. Texas accepts boat and airboat transports electronically with a short description of the client’s physical condition in the comment field. When the condition cannot be documented that way, the claim goes on paper with supporting records.
3. Bill one unit per line. The Medicaid NCCI practitioner file for October 1 to December 31, 2026 sets the A0999 limit at 1 unit. Medicaid tests each line separately, and a line over the limit is denied in full.

How state Medicaid programs use A0999

State Medicaid programs fill A0999 with their own services, so the code means something different in each one.

• Florida. The January 1, 2025 Transportation Services Fee Schedule lists A0999 with modifier QN as “Negotiated Transportation Service,” paid at a negotiated amount and only with prior authorization, in both the emergency and non-emergency ground groups. HCPCS itself defines QN as an ambulance service furnished directly by a provider of services, so the label is Florida’s own. The Florida rate reference has the rest of that schedule.
• Texas. The October 2026 Ambulance Services Handbook requires boat or airboat transports to be billed as A0999, together with ground mileage code A0425. The code also sits on the handbook’s list of emergency transport codes that take the ET modifier.
• Arkansas. The transportation fee schedule (run date May 13, 2026) prices the plain code at $0.00, which it says means manually priced. Two modifier lines pay crew time: A0999-U1 at $10.43 for an air nursing crew’s ground transport and A0999-U2 at $8.77 for an air paramedic crew’s, each per 15 minutes. The provider manual caps that crew ground time at $1,000 per round-trip flight.
• Oregon. The Medical Transportation Services Provider Guide (last updated December 22, 2025) lists A0999 for transportation brokers, alongside A0130 for wheelchair cars and vans and T2005 for stretcher cars and vans.
• Mississippi. The September 2026 comprehensive fee schedule puts A0999 on its non-covered tab, the list of codes not covered for any line of service.

Not a code for van trips

A0999 sits in the ambulance range. Wheelchair and stretcher van rides have codes of their own, such as A0130 and T2005, and the NEMT billing codes guide lists them by service. Oregon shows a program can still assign A0999 to a non-ambulance purpose. Before any van company puts it on a claim, get the payer’s instruction in writing and keep it with your billing setup. The CMS-1500 guide covers the rest of the paper claim.