CO-198 Denial Code: Service exceeded the approved authorization

What CO-198 means

CO-198 says an authorization existed but this service went beyond what it approved - more visits or units than were granted, or a date of service outside the approved window. That makes it different from CO-197, which fires when no authorization was obtained at all. Because it posts as a CO adjustment, the balance is a provider write-off, not patient responsibility. It is often recoverable: payer usage counts can be wrong, claims can cite the wrong auth details, and many plans will extend an authorization retroactively with clinical justification.

Common causes

• The authorization covered a set number of visits or units and this claim went past them.
• The date of service fell outside the authorization's approved date range.
• The authorization was approved for a different CPT code, provider, or site than what was billed.
• Multiple providers or departments drew from the same authorization without tracking shared usage.
• The payer's count of used visits is out of sync with yours - a corrected or duplicate claim double-counted usage.

How to fix it

• Pull the original authorization and compare its approved units, dates, CPT codes, and provider against the claim.
• If the claim actually fell within the approved limits, appeal with the authorization letter and a visit-by-visit usage log.
• If a claim detail (CPT, rendering NPI, DOS) simply does not match the authorization, correct the claim and resubmit.
• If the limits truly ran out, ask the payer about a retroactive extension or additional units with clinical justification - many plans allow it.
• If nothing is recoverable, post the contractual write-off; do not bill the patient.

How to prevent it

• Track remaining authorized visits and units in your PM system and alert staff before the last approved visit.
• Request extensions before the authorization expires or runs out, not after the extra visits happen.
• At scheduling, confirm each visit still falls inside the authorization's date range and unit count.
• When multiple providers share one authorization, centralize usage tracking so no one over-draws it.

Appeal potential

Appeal letter template

Fill in the bracketed fields, attach your supporting documentation, and send through the payer's appeal channel. This is a starting point — adjust to your payer's requirements.

Re: Authorization Denial Appeal (CO-198) - Claim [Claim Number]

Patient: [Patient Name]   |   Member ID: [Member ID]
Date(s) of Service: [DOS]
Authorization Number: [Auth Number]

To Whom It May Concern:

Claim [Claim Number] was denied under CO-198 as exceeding the authorized services. Authorization [Auth Number], issued [Auth Date], approved [Number] [visits/units] of [Service/CPT Code] for [Approved Date Range]. Our records show only [X] of those [visits/units] had been used as of the date of service, so this claim fell within the approved limits. Enclosed are the authorization approval and a usage summary supporting this.

We request that the denial be overturned and the claim processed under authorization [Auth Number].

Sincerely,
[Your Name], [Practice Name]   |   [Phone]   |   [NPI/TIN]