Reading a HCPCS Explanation of Benefits (EOB)

The Explanation of Benefits (EOB) or Electronic Remittance Advice (ERA) is the response a payer sends after processing a claim. For each service line, it shows the submitted amount, the allowed amount, the payer's payment, any patient responsibility, and a reason code explaining any reduction or denial. When a HCPCS code is denied or paid at a reduced rate, the reason code is your starting point for determining the correct response. Look up unfamiliar codes in the HCPCS code browser to verify whether the code was active on the date of service.

Common denial reason codes on HCPCS claims include CO-97 (bundled/included in another code — typically an NCCI edit), CO-4 (modifier invalid for the service — modifier appended without clinical basis), CO-167 (benefit category doesn't apply), and CO-B15 (payment adjusted because the submitted code was not covered or valid). Each of these points to a specific root cause that requires a different correction.

When a service line is paid at a reduced amount rather than denied outright, the remittance may show that a modifier was removed (reducing the payment to the standard rate) or that the units were adjusted (if CMS edit logic detected a unit discrepancy). Compare the paid units and rate against your submitted claim to understand the adjustment before deciding whether to accept it or appeal.

For J-code drug claims, the remittance will sometimes show a CARC 16 (claim/service lacks information needed for adjudication) when the NDC is missing or invalid. This is a correctable denial — resubmit with the correct NDC from the NDC lookup tool. EDI billing teams should confirm that their clearinghouse is populating the NDC loop (2410) correctly on the 837P transaction.