CAS segment of the 835, immediately before the CARC. There are four, and they answer one question: who bears this dollar?
The four codes
Why this is the highest-stakes field in the 835
Group code mapping determines your patient ledger.- Posting a PR amount as CO means you never bill a patient who owes you money. Pure, silent revenue loss, and it doesn’t show up in any denial report.
- Posting a CO amount as PR means you bill a patient for something your contract says they don’t owe. That is balance billing: a contract breach, a regulatory problem in many states, and a patient complaint.
CO, contractual obligation
The most common group code. The provider absorbs the amount because the participation agreement says so.
CO-197 is the one people get wrong. It is tempting to bill the patient for a service the payer refused over a missing authorization. You cannot — the group code says contractual obligation, meaning the practice bears it. The patient did nothing wrong.
PR, patient responsibility
The patient owes it. Move it to the patient ledger and into the statement cycle.OA, other adjustment
Used where neither CO nor PR applies. Frequently informational, or a transfer.PI, payer initiated reductions
The payer reduced payment based on its own determination, not a contractual term. These are the most likely to be appealable, because there is a payer decision to contest rather than a contract term to accept. Less common than the other three. When you see PI, look at it, it often represents a determination worth challenging.Quick reference: can I bill the patient?
Configuration checklist
For your auto-posting setup:- CO → contractual adjustment write-off account
- PR → patient ledger, into the statement cycle
- OA-23 on a secondary claim → informational, not an adjustment
- OA-100 → patient recovery workflow
- PI → review queue, not auto-write-off
- Any group code with a $0 payment and a denial CARC → denial queue, not write-off
- PLB segments → handled separately from claim-level adjustments