CO 186 denial code

Claim adjustment reason code 186. Often reported as CO 186.

Level of care change adjustment

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 186 means

Payment was adjusted because the patient's level of care changed during the period billed.

The payer priced part of the claim at a different level of care than billed, for example because the patient moved between care levels during a stay.

Check the dates of each level of care against the claim and the record. Splitting the claim correctly by level of care often resolves it.

Group codes seen with 186

On a remittance, 186 comes after a group code. These are the ones it is most often reported with:

• CO 186 (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

• The patient moved between levels of care and the claim did not show the change.
• The payer's review found a lower level of care was appropriate for part of the stay.
• Revenue codes or dates on the claim did not match the levels of care given.

What to do next

1. Compare the levels of care and dates in the record with the claim.
2. Correct the claim to show each level of care for its dates and resubmit.
3. Appeal with clinical records if the higher level of care was needed.

Related codes

• 150 (reason code) Records do not support level of service
• 152 (reason code) Records do not support length of service