COB & dual-eligibility

Outcome

You understand at a glance which payer pays first for any given service date, how secondary and tertiary claims will fall out, and where to confirm Medicaid last-resort and CMS Medicare-Secondary-Payer rules are firing.

Prerequisites

Scope	What it lets you do
clinical.member.read	Read the member's coverage list
billing.cob.read	View the COB waterfall preview

A member with at least one active coverage policy. Members with only one coverage have no COB to display.

What COB is

Coordination of Benefits is the rule set that decides which of a member's several insurances pays first, second, and so on. Most adjudication happens upstream at the payer; the platform's job is to:

1. Decide the order correctly.
2. Generate secondary / tertiary claims automatically once the primary adjudicates.
3. Enforce Medicaid last resort and CMS Medicare-Secondary-Payer matrices so we never bill a payer ahead of one who must pay first.

Where to view it

/members/:id → Coverage tab. The top of the tab shows a compact COB waterfall preview:

Each box is interactive — hover for the rule that placed the payer in that position, click for the underlying contract and program config.

Dual-eligible members

A member with both Medicare and Medicaid is dual-eligible. The Coverage tab header shows a badge:

• Dual-eligible (QMB) — full Medicaid wraparound; cost-sharing is paid by Medicaid.
• Dual-eligible (SLMB / QI / QDWI) — partial Medicaid help.
• Dual-eligible (full) — Medicaid covers Medicare's gap.

Click the badge for an explainer panel showing exactly what Medicaid will pay vs what falls to the patient.

How payer order is decided

The platform applies these rules in order:

1. Explicit member coverage priority — what the Coverage tab already shows.
2. CMS Medicare-Secondary-Payer matrix — for Medicare beneficiaries with a working aged spouse, ESRD, etc., MSP rules can demote Medicare below another payer regardless of stated priority.
3. Medicaid last resort — federal rule. Medicaid is forced to last regardless of stated priority.
4. Payer-priority rules — tenant configuration that overrides for contractual reasons (rare).

The COB waterfall preview shows the result; the per-box hover shows which rule placed the payer.

How secondary claims fall out

Once the primary payer's ERA arrives:

The COB module:

• Snapshots the primary's adjustments onto the original claim (remittance_adjustment rows).
• Builds the secondary 837 with 2320 CAS (claim-level) and 2430 SVD/CAS (line-level) loops carrying the primary's adjustments.
• Resumes pending waterfalls when a primary's ERA was previously DENIED or PENDED and later resolves.
• Auto-triggers tertiary when the secondary's 835 arrives.

You do not run any of this by hand — the platform watches every inbound 835 and generates the next-tier claim automatically. The detail page just shows you what happened.

Steps to inspect a COB chain

1. Open the member at /members/:id. The Coverage tab badges show multi-coverage and dual-eligibility status.

2. Click any specific claim in the Claims tab. The claim detail page has a Relationships tab that shows the parent and child claims with the COB role on each edge.

3. Click into the COB waterfall (Coverage tab) for a specific encounter date. The preview re-runs the COB selection on demand.

Validation

Check	Expected
Dual-eligible badge present when member has Medicare + Medicaid	Yes.
COB waterfall puts Medicaid last for a dual-eligible	Yes — Medicaid-last-resort rule fires.
Secondary claim auto-generated after primary 835 posts	Yes — appears in the Relationships tab on the original claim.
Tertiary claim auto-generated after secondary 835 posts	Yes — same chain extended.

Troubleshooting

Symptom	Cause	Fix
Secondary claim never built	Primary's 835 was DENIED or PENDED	Once the primary resolves to PAID/PARTIAL, the platform resumes the waterfall automatically.
Medicaid is showing as primary	Member has only Medicaid registered, or other coverages are termed	Add the missing Medicare / commercial coverage on the Coverage tab.
MSP matrix not firing	Member's working-aged-spouse / ESRD context is missing	Edit Coverage and add the relevant context fields.
Tertiary claim built but expected payer is excluded	Excluded as ancestor in the waterfall (the platform refuses to bill the same payer twice in a chain)	Confirm the coverage list — likely the same payer is listed twice with different priorities.

Next

6.3 — Audit log lookup (HIPAA pulls)