Medicare, Claims, Denials, Patient Responsibility and Revenue Cycle Management
In Part 1, we looked at the basic concept of Coordination of Benefits and learned why identifying the correct primary and secondary insurance is so important.
In this part, we will move from the basic concepts into situations that can be more challenging for medical billers.
One of the most important areas is Medicare Secondary Payer (MSP).
Medicare beneficiaries may have other coverage through an employer, workers’ compensation, automobile insurance, liability insurance, or other sources. In these situations, Medicare may not always be the first payer.
This is why billers need to understand not only commercial COB but also the circumstances in which Medicare becomes secondary.
We will also look at what happens after the primary payer processes a claim, how the secondary claim is submitted, how to read the EOB/ERA, and how COB-related denials can be worked effectively.
Medicare Secondary Payer
Medicare Secondary Payer, commonly referred to as MSP, refers to situations where Medicare does not pay first because another payer has primary responsibility.
A common mistake is assuming:
“The patient has Medicare, so Medicare should be billed first.”
That is not always correct.
The patient’s employment status, employer size, disability status, ESRD status, accident circumstances, and other factors can affect payer responsibility.
Therefore, Medicare patients should be screened carefully for other coverage.
Common Medicare Secondary Payer Situations
Some important MSP situations include:
- Working Aged.
- Disability.
- End-Stage Renal Disease (ESRD).
- Workers’ Compensation.
- Automobile or No-Fault Insurance.
- Liability Insurance.
Each situation has different rules, so the biller should verify the applicable requirements rather than applying one rule to every Medicare patient.
Working Aged Situation
A Medicare beneficiary may continue working after becoming eligible for Medicare.
If the patient has employer-sponsored group health coverage, the employer’s plan may be primary in certain circumstances, with Medicare secondary.
Employer size and applicable Medicare rules are important when determining responsibility.
Example
Mary is 67 and still working.
She has:
- Medicare.
- Employer-sponsored group health insurance.
The employer plan may be primary depending on the applicable circumstances, while Medicare may be secondary.
The biller should verify the patient’s MSP information rather than automatically billing Medicare first.
Medicare and Disability
A patient may qualify for Medicare because of disability and also have coverage through an employer group health plan.
In these cases, Medicare may be secondary depending on the applicable MSP rules.
Again, the important lesson for a biller is:
Do not determine payer order based only on the patient’s Medicare status.
Review the available coverage and applicable MSP information.
ESRD and the 30-Month Coordination Period
End-Stage Renal Disease is another important MSP situation.
Patients with ESRD may have Medicare and another group health plan.
There is a specific coordination period associated with ESRD during which the group health plan may generally pay before Medicare under applicable rules.
The 30-month period is important because payer responsibility can change after the coordination period.
Example
A patient with ESRD has:
- Employer group health coverage.
- Medicare.
The biller should determine where the patient is within the applicable ESRD coordination period.
Billing Medicare as primary without checking this information can result in an avoidable denial.
Workers’ Compensation
Workers’ compensation claims are different from ordinary health insurance claims.
If a patient’s injury is work-related, workers’ compensation may be responsible for the medical treatment.
Example
A warehouse employee injures their back while lifting a heavy box at work.
The patient visits a physician for treatment.
The biller should determine whether the injury is work-related and obtain the appropriate workers’ compensation information.
Important information may include:
- Workers’ compensation carrier.
- Claim number.
- Date of injury.
- Employer information.
- Adjuster information.
- Authorization requirements.
If the claim is incorrectly billed to the patient’s regular health insurance, the health plan may deny the claim because another payer is responsible.
Automobile and No-Fault Insurance
Medical services related to an automobile accident may involve automobile or no-fault insurance.
For example, a patient is injured in a car accident and receives emergency treatment.
Before billing regular health insurance, the provider may need to determine whether automobile insurance is responsible for the medical expenses.
The biller should gather relevant information such as:
- Date of accident.
- Accident-related diagnosis or reason for visit.
- Automobile insurance information.
- Claim number.
- Attorney information, if applicable.
- Applicable state and payer requirements.
The exact processing rules can vary, so the biller should follow the applicable payer requirements.
Liability Insurance
Another situation involves liability insurance.
For example, a patient is injured because of an incident involving another party.
Depending on the circumstances, a liability insurer may have responsibility for the medical expenses.
Again, proper documentation and payer verification are important.
The biller should avoid automatically billing the patient’s regular health insurance without investigating whether another payer has primary responsibility.
Medicare + Employer Insurance: Practical Example
Consider the following situation:
John is 68 years old and continues working.
He has:
- Medicare.
- Employer-sponsored health insurance.
John visits a physician for a medical condition unrelated to an accident.
The biller should first determine the applicable MSP situation.
If the employer plan is primary, the claim is submitted to the employer plan first.
After the employer plan processes the claim, the remaining eligible amount may be submitted to Medicare if appropriate.
This is a good example of why eligibility verification and MSP screening are essential before claim submission.
Primary and Secondary Claim Processing
Once the primary payer has been identified, the claim follows a specific sequence.
Basic Process
Patient Visit
↓
Insurance Verification
↓
Identify Primary Payer
↓
Submit Claim to Primary
↓
Primary Adjudication
↓
Receive EOB/ERA
↓
Determine Remaining Eligible Balance
↓
Submit to Secondary
↓
Secondary Adjudication
↓
Post Payment
↓
Bill Patient for Appropriate Remaining Responsibility
This sequence helps prevent unnecessary denials and incorrect patient billing.
Reviewing the Primary EOB/ERA
After receiving the primary payer’s EOB or ERA, the biller should not simply look at the payment amount.
The entire claim outcome should be reviewed.
Important fields include:
- Billed Amount: The amount originally submitted by the provider.
- Allowed Amount: The amount recognized by the payer under its rules or contract.
- Insurance Payment: The amount paid by the primary payer.
- Adjustment: The amount that cannot be collected from the payer or patient because of contractual or other applicable adjustments.
- Deductible: The portion assigned to the patient’s deductible.
- Coinsurance: The percentage of the allowed amount assigned to the patient after applicable deductible requirements.
- Copayment: A fixed amount the patient may owe for a covered service.
- Denial: An amount that the payer did not reimburse, along with the applicable reason.
The EOB/ERA is therefore a roadmap for determining what should happen next.
Example: Primary and Secondary Insurance
Let’s take a simple example.
A provider submits a claim for $500.
The primary payer determines:
- Billed amount: $500
- Allowed amount: $400
- Insurance payment: $320
- Patient responsibility: $80
The provider receives the EOB.
If the patient has secondary insurance, the claim may then be submitted to the secondary payer along with the primary payer’s adjudication information.
Suppose the secondary payer determines that it can pay $60 of the remaining eligible responsibility.
The patient’s final responsibility may then be reduced to the amount that remains according to the applicable secondary benefits and COB rules.
The important point is that the biller should not simply bill the patient the entire unpaid balance after primary insurance.
The secondary insurance must be given an opportunity to process the claim when appropriate.
Crossover Claims
A crossover claim is a claim that is transferred from one payer to another for additional processing when the applicable arrangement supports that process.
Medicare claims are a common example where crossover arrangements may apply.
When crossover processing occurs, the provider may not need to manually submit the claim to the secondary payer.
However, billers should still monitor the claim.
If the secondary payer does not receive the claim or does not process it as expected, appropriate follow-up may be required.
Common COB Denials
COB-related denials are common in medical billing.
Some examples include:
“Other Insurance is Primary”: The payer has information indicating that another insurance company should be billed first.
“Coordination of Benefits Required”: The payer needs additional information regarding other coverage before processing the claim.
“Coverage Terminated”: The insurance plan is no longer active.
“Submit to Other Payer”: The claim was submitted to an incorrect payer.
“Duplicate Claim”: The payer may have already received the claim or processed a similar claim.
Understanding the denial message is the first step toward resolving the problem.
COB Denial Resolution Workflow
A practical denial workflow can be:
Review Denial
↓
Check Patient Insurance Information
↓
Verify Eligibility
↓
Identify Other Coverage
↓
Determine Correct Payer Order
↓
Check Primary EOB if Applicable
↓
Correct Claim Information
↓
Submit to Correct Payer
↓
Follow Up
This process should be documented according to the organization’s workflow and payer requirements.
Common COB Mistakes Made by Billers
Mistake 1: Assuming Medicare Is Always Primary
Medicare can be secondary in several situations.
Mistake 2: Not Asking About Other Coverage
A patient’s insurance profile may not always contain complete information.
Mistake 3: Ignoring Accident Information
An accident-related claim may involve auto insurance, workers’ compensation, or liability insurance.
Mistake 4: Billing the Secondary Payer Too Early
The secondary payer may require the primary payer’s adjudication information.
Mistake 5: Not Reviewing the EOB
The EOB contains important information needed for secondary billing and patient responsibility.
Mistake 6: Billing the Patient Immediately
A balance remaining after primary insurance does not automatically mean the patient must pay it.
COB and Patient Responsibility
One of the most important responsibilities of a medical biller is to ensure that the patient is billed correctly.
Suppose the provider charges $1,000.
The primary payer processes the claim and leaves $200 as patient responsibility.
The patient has secondary insurance.
The biller should not automatically send a $200 bill to the patient before allowing the secondary insurance to process the claim, when applicable.
After the secondary payer processes the claim, the remaining amount should be reviewed.
Only the amount that is legitimately the patient’s responsibility should be billed.
This protects the patient and helps maintain accurate accounts receivable.
COB and Revenue Cycle Management
COB directly affects the revenue cycle.
When insurance is correctly identified at the beginning of the process, claims can move smoothly through the billing cycle.
When COB information is incorrect, the impact can spread across multiple departments.
For example:
Incorrect Insurance Information
↓
Wrong Payer Billed
↓
Claim Denied
↓
AR Increased
↓
Additional Follow-Up
↓
Payment Delayed
↓
Possible Patient Confusion
This is why COB should not be considered only a billing-office issue.
It begins at registration and eligibility verification and continues through claims, payment posting, denial management, and patient billing.
Revenue Leakage Caused by COB Errors
Revenue leakage occurs when the provider fails to collect reimbursement that should have been received.
COB errors can contribute to revenue leakage through:
- Claims sent to the wrong payer.
- Missed secondary claims.
- Incorrect insurance sequencing.
- Failure to follow up on denials.
- Incorrect patient responsibility.
- Timely filing issues.
- Unresolved other-insurance information.
A claim that could have been paid but remains unresolved creates unnecessary financial loss.
Therefore, strong COB processes can improve both cash flow and revenue integrity.
Practical Case Study 1: Commercial Insurance
A patient has two commercial insurance plans.
The patient provides both insurance cards.
The biller verifies eligibility and determines:
- Plan A = Primary.
- Plan B = Secondary.
The claim is submitted to Plan A.
Plan A processes the claim and sends an EOB showing a patient responsibility amount.
The biller reviews the EOB and submits the remaining eligible amount to Plan B.
Plan B processes the claim.
The account is then reviewed to determine the final patient responsibility.
Lesson
The key is not simply having two insurance cards. The important part is establishing the correct payer sequence.
Practical Case Study 2: Medicare and Employer Coverage
A Medicare beneficiary continues to work and has employer-sponsored insurance.
The provider’s billing team identifies the employer plan and Medicare.
Instead of automatically billing Medicare first, the biller reviews the patient’s MSP information and applicable circumstances.
The employer plan is determined to be primary.
The claim is submitted accordingly.
After primary processing, Medicare is billed as secondary when appropriate.
Lesson
Medicare eligibility does not automatically mean Medicare is the primary payer.
Practical Case Study 3: Work-Related Injury
A patient visits a physician because of an injury sustained at work.
The registration team identifies the injury as work-related.
The biller obtains the workers’ compensation information.
Instead of billing the patient’s regular commercial insurance immediately, the claim is directed according to the applicable workers’ compensation process.
Lesson
Always ask whether the medical service is related to an accident or work-related injury.
Practical Case Study 4: Automobile Accident
A patient is treated following an automobile accident.
The patient has regular health insurance but also provides automobile insurance information.
The biller identifies the accident and investigates the applicable payer responsibility.
The claim is then submitted according to the appropriate insurance and legal requirements.
Lesson
Accident-related claims require additional attention because another payer may be responsible.
COB Checklist for the Complete Billing Process
A biller can use the following checklist:
Before Claim Submission
Identify all insurance coverage.
- Verify eligibility.
- Confirm effective dates.
- Confirm subscriber information.
- Determine primary payer.
- Check for Medicare/MSP considerations.
- Check for accident or workers’ compensation involvement.
After Primary Adjudication
- Review EOB/ERA.
- Confirm allowed amount.
- Confirm payment.
- Review adjustments.
- Review deductible, copayment, and coinsurance.
- Identify remaining eligible balance.
- Determine whether secondary billing is required.
Before Patient Billing
- Confirm secondary insurance processing.
- Review final patient responsibility.
- Ensure contractual adjustments are correctly posted.
- Bill only the amount legitimately assigned to the patient.
The Golden Rule of COB
A simple way to remember the entire COB process is:
Identify → Verify → Sequence → Bill → Review → Coordinate → Resolve
Identify: Find all insurance coverage.
Verify: Confirm that the coverage is active and obtain the necessary information.
Sequence: Determine which payer is primary, secondary, and tertiary when applicable.
Bill: Submit the claim to the correct payer.
Review: Study the EOB or ERA carefully after adjudication.
Coordinate: Submit the claim to the secondary payer when appropriate.
Resolve: Work denials, unpaid balances, and other COB issues until the account reaches the correct final status.
Final Thoughts
Coordination of Benefits may look complicated at first, particularly when Medicare, employer coverage, accidents, workers’ compensation, or multiple commercial plans are involved.
But the basic principle remains simple:
The right claim must reach the right payer in the right order.
A good medical biller does not simply look at an insurance card and submit a claim. A good biller asks questions, verifies information, understands payer responsibility, reviews the EOB/ERA, and follows the claim until the account is correctly resolved.
COB also shows why different areas of the revenue cycle are connected.
- Registration affects eligibility.
- Eligibility affects payer sequencing.
- Payer sequencing affects claim submission.
- Claim submission affects payment.
- Payment affects secondary billing.
- Secondary billing affects patient responsibility.
And all of these ultimately affect the provider’s revenue cycle.
When COB is handled correctly, providers can reduce avoidable denials, improve reimbursement, minimize incorrect patient balances, and maintain a cleaner accounts receivable.
For medical billing professionals, therefore, COB is not just another billing rule to memorize. It is a practical skill that directly influences claim accuracy, denial prevention, patient satisfaction, and revenue cycle performance.
Final Reminder
Whenever a patient has multiple insurance coverages, remember:
- Don’t assume. Verify.
- Don’t bill randomly. Sequence correctly.
- Don’t stop after primary payment. Coordinate.
- Don’t bill the patient too quickly. Review the final responsibility.
That mindset can make a significant difference in accurate and efficient medical billing.
For the fundamentals of primary and secondary insurance, see Coordination of Benefits in Medical Billing – Part 1.