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N159 Remark Code: Mileage Without Patient on Board

N159 means payment for ambulance mileage was denied or reduced because mileage is not covered when the patient is not in the ambulance. Only the miles traveled with the patient on board (loaded mileage) are payable.

Quick facts

Code
N159 (RARC N159)
Status
Active In use since February 28, 2003.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): Mileage without the patient aboard is not payable and cannot be billed to the patient.
Official description
Payment denied/reduced because mileage is not covered when the patient is not in the ambulance.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N159 means

Ambulance payment has two parts: a base rate for the service level and mileage. Payers cover only loaded mileage, the miles traveled with the patient aboard. N159 tells you the mileage on the claim included, or appeared to include, distance without the patient, so it was reduced or denied.

Common causes

  • The crew recorded odometer readings from dispatch rather than from patient pickup.
  • Mileage for the return trip to base was added.
  • A trip where the patient was not transported was billed with mileage.
  • Units were entered as total trip mileage because the software default was wrong.
  • Rounding or decimal errors inflated the mileage count.

How to fix it

  1. Review the run report for odometer readings at pickup and at arrival at the destination.
  2. Recalculate loaded miles and apply the payer’s rounding rule.
  3. Submit a corrected claim with the right units in CMS-1500 box 24G, resubmission code 7 in box 22, and the original claim number.
  4. If the mileage was already correct, appeal with the run report and a map showing the route.

How to prevent it

Capture pickup and drop-off odometer readings or GPS data in your electronic patient care report, and have billing software calculate mileage from those points only. The units of service guide covers other unit-count denials.

Codes that may appear with N159

  • CO-96 (Non-covered charge(s).): A non-covered charge for the unloaded miles.
  • CO-151 (Payment adjusted because the payer deems the information submitted does not support this many/frequency of services.): The information does not support the number of units, here the mileage count.
  • CO-16 (Claim/service lacks information or has submission/billing error(s).): Used when mileage information on the claim is missing or inconsistent.
  • N157 (Transportation to/from this destination is not covered.): Transport to or from the destination is not covered.
  • N158 (Transportation in a vehicle other than an ambulance is not covered.): Transport in a non-ambulance vehicle is not covered.
  • N114 (During the transition to the Ambulance Fee Schedule, payment is based on the lesser of a blended amount calculated using a percentage of the…): Explains blended ambulance payment during the fee schedule transition.

N159 FAQ

What is loaded mileage?

The distance from where the patient was picked up to where they were dropped off, while they were in the ambulance. Travel to reach the patient and return trips without them are not included.

How is mileage reported?

As units on the mileage line, typically statute miles, rounded according to payer rules. Medicare uses HCPCS mileage codes, such as A0425 for ground mileage.

What if the patient died en route or was not transported?

Special rules apply to those situations and vary by payer. Check the payer's ambulance policy before billing mileage.