COB information can be very complex within the 837:
...can be tracked in the nested structure of an 837. To display such a nested structure is a daunting task, as you can imagine. I still recommend that you fully understand the nesting of COB data.
On the Claim level, we find additional payers in the 2320 loops. Within the 837 EDI file, adjudication information is stored in either CAS segments or the Medicare, MIA (inpatient) and MOA (outpatient) segments. Specific amounts are similarly stored in the AMT segments. On the line level, each line can contain up to 25 different adjudication actions; SVD segments, which identify the payer and their amounts. Adjudication information is then written in multiple CAS segments and optionally, in the DTP segment, the adjudication date.
If the HIPAA Claim Master finds that a claim lists several payers, the claim preview screen will display the "COB" button.
The "COB Info" button
Click this button, and the following display appears:
Each payer is in one block. Any claim level adjudication will be displayed, listing adjustment group and adjustment reason.
Line level information is displayed on the following pages.
Notice the nested structure of the display. For each line, we see a recap of the line information, followed by payer information and possibly several lines of adjudication information.