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CO-173 Denial Code: Not Prescribed by a Physician

CO-173 means the payer denied the service or equipment because it was not prescribed by a physician, or the payer has no valid order from a qualified prescriber on file. It is common for DME, supplies, therapy, and other ordered services.

Quick facts

Code
CO-173 (CARC 173)
Status
Active In use since June 30, 2005; last modified July 1, 2013.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The supplier or provider is responsible for the denied amount without a valid order. It is not billable to the patient under a network contract.
  • PR (Patient Responsibility): Occasionally applied when the patient obtained the item without a prescription and the plan leaves the cost to the patient.
Official description
Service/equipment was not prescribed by a physician.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-173 means

CARC 173 reads “Service/equipment was not prescribed by a physician.” Many services and items are only covered when ordered: durable medical equipment, supplies, lab and imaging tests, home health, and therapy under some plans. If the payer can’t find a qualifying order, or the order came from someone who can’t prescribe that item, the claim is denied.

The payer may base this on the claim (no ordering provider reported, or an ordering NPI that isn’t eligible) or on a records review where no order was produced.

Example: a DME supplier delivers a wheelchair based on a phone request from a clinic, but never obtains the signed written order the payer requires. On review, the claim is denied CO-173.

Common causes

  • No written or electronic order in the file for the item or service.
  • Ordering provider missing from box 17/17b or the 837 ordering loop.
  • Ordering NPI not enrolled with the payer, or not of a type allowed to order.
  • Verbal order never signed or authenticated.
  • Self-referred services, where the patient requested an item or test without a prescriber’s order.
  • Order from an ineligible prescriber under the payer’s rules or state law.

How to fix it

  1. Locate the order. Check whether one exists, who signed it, and its date.
  2. If the order exists but wasn’t on the claim, add the ordering provider name and NPI in box 17 and 17b and submit a corrected claim (resubmission code 7).
  3. If the order exists but wasn’t sent on review, appeal with a copy of the signed order.
  4. If the ordering provider isn’t enrolled, ask the provider to enroll (Medicare requires ordering and referring providers to be enrolled) or obtain a valid order from an eligible prescriber, subject to timing rules.
  5. If there was never an order, the claim is generally not recoverable from the payer. Write off the CO amount.

How to prevent it

  • Don’t deliver or perform ordered services until a complete, signed order is in the file.
  • Verify the ordering provider’s NPI and enrollment at intake.
  • Capture ordering provider data in the claim automatically from the order. The Claims Validator can flag missing ordering-provider fields before submission.
  • Follow up on verbal orders until they are signed.
  • Train intake staff on which services need orders for each payer. See preventable denials.

Specialty notes

DME suppliers and independent labs are most affected. Outpatient PT/OT practices may see it where a plan requires a physician referral or signed plan of care.

Remark codes that may appear with CO-173

  • N455 (Missing Physician Order.): The physician order is missing entirely.
  • N456 (Incomplete/invalid Physician Order.): An order exists but is incomplete or invalid.
  • N265 (Missing/incomplete/invalid ordering provider primary identifier.): The ordering provider's NPI is missing or invalid on the claim.
  • N574 (Our records indicate the ordering/referring provider is of a type/specialty that cannot order or refer.): The ordering or referring provider's type cannot order or refer this service.
  • CO-174 (Service was not prescribed prior to delivery.): A prescription existed, but it was written after delivery.
  • CO-175 (Prescription is incomplete.): A prescription exists but is incomplete.
  • CO-183 (The referring provider is not eligible to refer the service billed.): The referring provider is not eligible to refer the service.
  • CO-16 (Claim/service lacks information or has submission/billing error(s).): Missing claim data, such as an ordering NPI, when the order itself is not in dispute.

CO-173 FAQ

Does the prescriber have to be a physician?

It depends on the payer and the item. Many programs accept orders from nurse practitioners, physician assistants, or other qualified practitioners within state scope of practice. The official text says 'physician,' but payers apply their own rules.

Can I get a prescription after the fact and rebill?

For items that require an order before delivery, a later prescription usually doesn't cure the denial (that situation is CO-174). If an order existed but wasn't on the claim or in your file, get a copy and resubmit or appeal.

What claim fields show the ordering provider?

On the CMS-1500, box 17 (name with qualifier DK for ordering) and 17b (NPI). On the 837P, the ordering provider loop at the claim or line level.