What does indemnification adjustment mean on a remittance?

It is OA-121: the payer recorded an adjustment connected to the patient's outstanding responsibility rather than to the covered benefit. It is an accounting entry, not a denial and not a new patient balance, so do not bill the patient for it without checking where the amount already went.

Why did my claim pay less than the billed amount?

Usually because of CO-45, which writes off the difference between your charge and the contracted allowed amount. Other common reductions are CO-59 for multiple procedures in one session and OA-23 when a secondary payer accounts for the primary's payment. Compare the allowed amount with your contract to tell a correct reduction from an underpayment.

Payment reduction codes: why a claim paid less than billed

When a claim pays but for less than the charge, the adjustment lines tell you why - and most of them are correct. CO-45 is the routine one: the charge is higher than the contracted allowed amount, and an in-network provider writes the difference off. CO-59 reduces secondary procedures under multiple procedure rules. OA-23 is a secondary payer accounting for what the primary already paid. OA-121 records an indemnification adjustment tied to outstanding patient responsibility, and PI-223 an adjustment that a federal, state, or local law requires when no more specific code exists.

Also described as: underpayment; contractual adjustment; write-off; multiple procedure reduction; indemnification adjustment.

The 5 codes and what separates them

CO-45 - Charge exceeds the contracted fee schedule amount
The charge exceeds the allowed amount under the fee schedule or contract; the difference is written off, not billed to the patient.
Who pays: Provider
CO-59 - Payment reduced under multiple or concurrent procedure rules
Secondary procedures in the same session were paid at a reduced rate under multiple or concurrent procedure rules.
Who pays: Provider
OA-23 - Impact of prior payer's adjudication
A secondary payer reduced its payment by what the primary payer already allowed or paid.
Who pays: Neither - adjustment
OA-121 - An indemnification adjustment was applied
The payer applied an adjustment connected to outstanding patient responsibility. The balance has already moved, so it is not a new patient balance.
Who pays: Neither - adjustment
PI-223 - An adjustment required by federal, state, or local law
A law or regulation required the adjustment and no more specific code covers it; the remark codes and the payer's notice say which.
Who pays: Provider

How to tell which one you have

Start by comparing the allowed amount with your contracted rate for the code. If they match, a CO-45 write-off is correct and the only open question is the patient's share. If the allowed amount is below contract, that is an underpayment worth disputing with provider relations, whatever the code says. CO-59 is worth checking only for sequencing - the highest-valued procedure should be paid in full. OA-121 is the one most often mishandled: it is not a new patient balance, so billing it to the patient risks charging them twice.

Frequently asked questions

What does indemnification adjustment mean on a remittance?: It is OA-121: the payer recorded an adjustment connected to the patient's outstanding responsibility rather than to the covered benefit. It is an accounting entry, not a denial and not a new patient balance, so do not bill the patient for it without checking where the amount already went.
Why did my claim pay less than the billed amount?: Usually because of CO-45, which writes off the difference between your charge and the contracted allowed amount. Other common reductions are CO-59 for multiple procedures in one session and OA-23 when a secondary payer accounts for the primary's payment. Compare the allowed amount with your contract to tell a correct reduction from an underpayment.

Other denial reasons

Out of network No prior authorization Not medically necessary Service not covered Bundled or not paid separately Coding mismatch or invalid code Patient not eligible or coverage ended Another payer is responsible Missing information, duplicate, or late filing Provider not eligible or not credentialed Benefit or unit limit reached Deductible, coinsurance, or copay

Every denial code in one table

Last reviewed October 3, 2026.

These are original plain-English summaries written for reference, not the official X12 code descriptions. Payer handling of any code varies by contract - always verify against the remittance advice and your payer agreement before adjusting a claim.