Claim denied for primary EOB

Denial Code 163: Attachment or Documentation Not Received – How to Work This Denial (Primary EOB Missing)

Denial code 163 is a very common denial in medical billing and AR follow-up. This denial occurs when the insurance company says:

“Attachment/other documentation referenced on the claim was not received.”

In most cases, this means the payer is asking for the Primary Insurance EOB (Explanation of Benefits) or payment details from the primary insurance.

Let’s understand how to work denial code 163 step-by-step in a simple way.

What Does Denial Code 163 Mean?

Denial code 163 indicates the payer needs supporting documents, such as:

• Primary insurance EOB
• Proof of payment
• Coordination of benefits information
• Other referenced claim attachments

This happens mostly when:

• The payer is secondary insurance
• They require primary paid EOB
• The EOB was not sent along with the claim

On-Call Scenario: How to Talk to the Insurance Representative

When you call the insurance for this denial, follow this workflow.

Step 1: Confirm the Denial and Denial Date

Start the call with:

“The claim is denied for missing primary EOB. May I get the denial date?”

This helps in documenting and tracking timely filing limits.

Step 2: Check Whether This Insurance Is Primary or Secondary

Now check your system eligibility/insurance order.

Ask:

“In your system, is this insurance listed as primary or secondary?”

This decides your next action.

If the Insurance Is Listed as PRIMARY

If the payer says they are primary, then you must verify what primary coverage they have on file.

Ask:

“Could you please tell me which insurance is primary insurance on your end?”

If Representative Provides the Primary Insurance Details

Collect these details:

• Policy ID
• Payer ID
• Primary insurance mailing address (or fax number)
• Claim number & call reference number

Ask:

“What is the policy ID, payer ID, and mailing address for the primary insurance?”
“May I have the claim number and call reference number?”

If Representative DOES NOT Provide Primary Insurance Details

Then you should:

• Check your billing system for other insurance
• Check patient payment history (may show primary payer)
• Check payer web portal (if available)

If you find another active insurance:

• Verify eligibility
• Update insurance order (primary/secondary)
• Resubmit to correct primary

If no other insurance is active:

• Release claim to patient (or follow client instructions)

If the Insurance Is Listed as SECONDARY

If the payer is secondary, then the most important step is:

Check if primary payment exists.

Ask/verify:

• Is primary payment received?
• Is primary EOB processed?

Case 1: Primary Payment is Received/Processed (YES)

Now check the claim form:

CMS 1500 – Box 29

(Shows paid amount by primary)

If paid amount is showing in Box 29, it means:

Primary paid details were already sent on the claim form.

Now ask the rep:

“Could you please reprocess the claim as primary payment details are already sent in Box 29?”

If Rep Says They Still Did Not Receive It

Then you must send EOB separately.

Ask:

“What is the fax number or mailing address and what is the time limit to send the EOB?”
“May I have the claim number and call reference number?”

Case 2: Primary Payment is NOT Received/Processed (NO)

Then you must follow up with the primary insurance first.

Action steps:

1. Follow up with primary payer
2. Get primary EOB/payment processed
3. Then bill secondary

This is mandatory because secondary will not process without primary EOB.

If Claim Is Sent for Reprocessing

If the rep agrees and sends the claim for reprocessing:

Ask:

“What is the TAT (Turnaround Time) for reprocessing?”
“May I have the claim number and call reference number?”

Document the TAT properly for future follow-up.

Important Notes for Working Denial 163

Here are key best practices:

Always Verify Primary Insurance Eligibility

If rep provides primary insurance details and you have web portal access:

• Check eligibility on portal
• Confirm if primary was active on DOS
• If inactive → ask payer for correct guidance / update responsibility

Always Check Paid Details in Forms

If primary has already paid, verify whether paid details are on the claim:

• CMS 1500 – Box 29
• UB04 – Locator 54

If not available → resend claim or submit EOB manually.

If Time Limit Has Passed

If EOB submission time limit already crossed:

• Write off charges OR
• Follow client instructions for next steps

Always Check Remark Codes

Sometimes denial 163 is generic, but the real issue is found in:

• Remark codes
• CARC/RARC codes

So always check denial codes + remarks and follow AR scenario tool accordingly.

Conclusion

Denial code 163 is mainly related to missing documentation — especially primary EOB. To resolve it successfully:

1. Confirm denial date
2. Identify if payer is primary or secondary
3. If secondary → ensure primary payment is processed
4. If primary paid details exist → request reprocessing
5. If not received → submit EOB via fax/mail within time limit
6. Always document claim number & call reference number