CO-109: Claim/service not covered by this payer/contractor

CO-109 usually means one of two things: (1) the claim was routed to the wrong insurer, or (2) another payer should have paid first under a coordination of benefits rule. Both are usually fixable without a full appeal.

What your letter emphasized

• Which insurer should be primary for the date of service
• Any coordination of benefits (COB) rules that apply (spouse's plan, Medicare, injury with third-party liability)
• Evidence of prior claim submission to the primary payer if the current payer is secondary
• The plan's obligation to explain which payer it thinks is responsible if not itself

What the insurer's likely response is

Reprocessing after COB update. If you update the plan's COB records to show the correct primary payer, the plan often reprocesses.

Clarification of the plan's COB position. The plan explains why it believes another payer is primary.

Upheld with no useful information. The plan reasserts CO-109 without helping you figure out the right payer. This is a bad response and worth escalating.

How to handle each outcome

Reprocessing: confirm the primary payer paid or denied first, then confirm the secondary payer processes the balance.

Clarification: if the plan says another payer is primary, contact that payer and submit the claim there. Save the response.

Uninformative uphold: file a state DOI complaint. Plans should not send you in circles.

Common CO-109 scenarios

Two commercial plans (COB). Under NAIC COB rules, the plan of the person whose birthday falls earlier in the calendar year is generally primary for dependent children (the "birthday rule"). For subscribers, their own plan is primary. Check both plans' COB rules.

Commercial plus Medicare. For most working-age Medicare beneficiaries with a group plan, the group plan is primary if the employer has 20 or more employees. For retirees, Medicare is primary. Rules for end-stage renal disease are different.

Commercial plus Medicaid. Medicaid is always the payer of last resort.

Injury from a third party. If the claim relates to an injury caused by a third party (car accident, slip and fall), the plan may want to know about the third-party liability. This can be resolved with a letter explaining the status.

Workers' compensation. If the injury was work-related, workers' comp is usually primary. The commercial plan may refuse to pay until workers' comp determination is made.

What to gather

• All insurance cards for anyone in the household
• Any prior EOBs from other payers
• Information about the injury or event, if third-party liability is involved
• Correspondence with the workers' comp carrier if applicable

Update COB with the plan

Every plan has a COB update process. Call member services and ask "how do I update my coordination of benefits information?" Provide:

• Current plan information
• Other insurance information (subscriber, plan name, effective dates)
• The relationship of each covered person to each subscriber

Once COB is updated, the plan should reprocess the claim on the next batch cycle (usually a few days to a couple weeks).

When it is not COB

Sometimes CO-109 means the claim was genuinely sent to the wrong insurer (a former plan, a plan for a different family member). In that case, ask the provider to resubmit to the correct plan.

Escalation

If the plan will not clarify, and the provider cannot help, state DOI complaint is the right next step for CO-109 stonewalls. External review does not usually apply because COB determinations are not medical-judgment decisions.