2.6 Commercial Insurance & Coordination of Benefits (COB)

Commercial Plan Types

Quick Answer: Commercial plans differ in how strictly they limit you to a network and whether you need a referral. When a patient has two plans, Coordination of Benefits decides which one pays first — and for a child covered by both parents, the Birthday Rule applies.

Commercial insurance is private coverage, usually offered through an employer or purchased individually on a marketplace. Billers must identify the plan type because it dictates network rules, referral and authorization requirements, and patient cost-sharing.

Comparing Plan Types

An HDHP pairs a high deductible with a tax-advantaged Health Savings Account (HSA). Patients pay most early costs out of pocket until the deductible is met. The EPO is the trap on this table: like an HMO it locks you to the network, but like a PPO it usually needs no referral.

Referral and Authorization

A referral is approval from a primary care provider (PCP) to see a specialist; HMO and POS plans typically require one. Prior authorization is the payer's advance approval of a specific service or drug and is separate from a referral. A patient can have a valid referral and still be denied for missing prior authorization on the procedure. Missing either one is a frequent denial reason.

In-Network vs Out-of-Network

In-network providers have a contracted rate with the plan, so the patient pays lower cost-sharing and the provider writes off the contractual adjustment. Out-of-network (OON) care, when covered at all, uses higher deductibles and coinsurance and may expose the patient to balance billing where state and federal law permit it. The federal No Surprises Act now bars balance billing for most emergency services and for out-of-network providers at in-network facilities, an increasingly tested protection. Billers also distinguish a copay (a fixed dollar amount per visit, e.g.

$30) from coinsurance (a percentage of the allowed amount, e.g. 20%) and from the deductible (the amount the patient pays before the plan begins to share costs).

Coordination of Benefits (COB)

Coordination of Benefits (COB) is the process of determining the payment order when a patient has more than one health plan. The primary plan pays first as if it were the only coverage; the secondary plan then considers the remaining balance, never paying more than it would have as primary.

Determining the Primary Plan

The Birthday Rule compares only the month and day of each parent's birthday, not the year — the older parent is not automatically primary. If both parents share the same birthday, the plan in effect longer is primary.

Medicare Secondary Payer (MSP) Hierarchy

Medicare follows a defined Medicare Secondary Payer (MSP) order. In general, an employer group health plan pays before Medicare for actively working beneficiaries (or a working spouse) at employers of 20+ (Working Aged) or 100+ for disability. Workers' compensation, no-fault, and liability insurance pay before Medicare for accident-related care. Misidentifying Medicare as primary when an MSP rule makes it secondary is a high-frequency exam item and a real-world overpayment risk.

Auto, No-Fault, and Liability Subrogation

When care results from an accident, auto, no-fault (Personal Injury Protection, PIP), or liability coverage is usually primary. If the health plan pays first, it may pursue subrogation — recovering its payment from the at-fault party or the liability settlement. Billers must capture accident details (date, cause, claim number) so claims route to the correct payer the first time.

Secondary Claim Mechanics

After the primary plan adjudicates, the biller submits to the secondary payer with the primary Explanation of Benefits (EOB) or electronic remittance advice (ERA) attached. The secondary plan applies its own benefits to the remaining balance but never pays more than it would have paid as primary — so the combined payment rarely exceeds 100% of the allowed amount. Any contractual write-offs taken by the primary in-network provider reduce what the patient and secondary owe. A frequent denial occurs when a biller bills the secondary plan without the primary EOB; the secondary has no way to coordinate and rejects the claim.

Putting COB Into Practice

Think of COB as a three-step decision: (1) identify every payer the patient has, (2) rank them using subscriber status, the Birthday Rule for dependent children, court decrees, active-versus-retiree rules, and the MSP hierarchy, then (3) bill in that order, attaching each prior payer's remittance. Getting the order wrong produces takebacks, duplicate-payment recovery, and delayed reimbursement. Capturing accurate coverage and accident information at registration is what lets the biller route the claim correctly the first time and protect both the patient and the practice from balance-billing and refund problems.