Verify patient insurance information at each visit
Insights / Denials
Secondary Insurance: Coordination of Benefits
Sriram Raghavan · August 2, 2026 · 6 min read
The short version
If you read nothing else on this page.
Accurately complete the CMS-1500 form, including primary and secondary insurance information
Follow the standard COB rules outlined in the CMS Medicare Claims Processing Manual
If your practice doesn't get the coordination of benefits right for patients with secondary insurance, you risk delayed or denied claims. Medicare and most payers require accurate COB information to process claims correctly. The Centers for Medicare and Medicaid Services (CMS) provides guidelines on COB in the Medicare Claims Processing Manual.
What is Coordination of Benefits?
Coordination of benefits (COB) is the process of determining which insurance plan is primary and which is secondary when a patient has multiple insurance plans. The primary plan pays its share of the costs first, and then the secondary plan pays its share. The National Association of Social Workers (NASW) and the American Medical Association (AMA) also provide guidance on COB.
How Does COB Work?
To get COB right, your team needs to verify patient insurance information at each visit, including the patient's primary and secondary insurance plans. The CMS-1500 form is used for Medicare and other insurance claims, and it includes fields for primary and secondary insurance information.
Why is COB Important?
Accurate COB information is crucial to avoid claim denials and ensure timely reimbursement. The Council for Affordable Quality Healthcare (CAQH) estimates that COB issues are a common cause of claim denials. The standard COB rules are outlined in the CMS Medicare Claims Processing Manual, and most payers follow these rules.
What Teams Get Wrong
Common mistakes in COB include not verifying patient insurance information at each visit, not accurately completing the CMS-1500 form, and not following the standard COB rules. The National Committee for Quality Assurance (NCQA) provides resources on COB and other topics related to healthcare quality.
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