CO 173 denial code

Claim adjustment reason code 173. Often reported as CO 173.

Not prescribed by a physician

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What 173 means

The payer will not pay because the service or equipment was not ordered by a physician as the plan requires.

Some services and items, such as equipment and supplies, need a physician's order. This code means the payer found no valid order from a physician for this claim.

Check whether an order exists and who signed it. If another practitioner ordered it, check the payer's rules on who may order this item.

Group codes seen with 173

On a remittance, 173 comes after a group code. These are the ones it is most often reported with:

• CO 173 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• No order was on file or sent with the claim.
• The order was signed by a practitioner the payer does not accept for this item.
• The ordering provider information was missing from the claim.

What to do next

1. Find the order and check who signed it and when.
2. Add the ordering provider details to the claim and resubmit.
3. Get a valid order from a qualified practitioner if none exists.

Related codes

• 174 (reason code) Not prescribed before delivery
• 175 (reason code) Prescription incomplete
• 184 (reason code) Ordering provider not eligible