CO-31 Denial Code: Why “Patient Cannot Be Identified” Happens and How to Fix It Fast

Important Points:

The CO-31 denial is one of the easiest claim rejections to avoid in medical billing. Most of the cases are caused by simple mistakes in demographics or eligibility that can be fixed with better front-end processes.

Keep in mind:

• Check eligibility early

• Make sure the patient data is correct
• Check automatically
• Keep an eye on patterns of denial
• Do something right away when you get a rejection

Providers can greatly cut down on “patient cannot be identified” denials and make the revenue cycle work better by using accurate registration, real-time verification, and expert denial management.

Claim denials are still one of the biggest problems in today’s revenue cycle management (RCM) world. The CO-31 denial, which is often called “Patient Cannot Be Identified,” is one of the most annoying and avoidable rejections.
It might look like a small mistake at first. But in reality, this denial can cause payments to be late by weeks, raise the cost of rework, and throw off cash flow. Even small mistakes in data can lead to big losses in revenue for billing teams that process hundreds or thousands of claims every day.

To raise clean claim rates and speed up payments, it’s important to know why CO-31 denials happen and how to fix them quickly. Let’s look at the reasons, the solutions, and the ways to avoid them.

What does it mean to have a CO-31 Denial?

A CO-31 denial happens when the payer can’t find the patient information on the claim in their insurance database.
Simply put, the insurance company can’t confirm who the patient is.
This usually results in:

• • Immediate denial of the claim
    • Delays in payment
    • Rewrite and send again
    • Higher costs for running the business
    • Lower rates of acceptance on the first try

CO-31 is a front-end denial because it comes from mistakes in demographics or eligibility. This means that it could have been avoided before submission.

Common Reasons for “Patient Cannot Be Identified” No:

Let’s look into the most common reasons why this patient can’t be identified denial.

1. Wrong Member or Subscriber ID

Even one wrong number in the insurance ID can make it impossible for payers to find the patient’s record. One of the main reasons is mistakes made when entering data by hand.
For example:

• Characters that are missing
  • Numbers that have been switched around
  • Old ID after renewing insurance

2. Names that don’t match

Names must be exactly the same as they are in the payer’s database.
Some common problems are:

• Nicknames and real names
  • Mistakes in spelling
  • No middle initials
  • Differences between married and maiden names

For example, “Robert Smith” vs. “Bob Smith” can cause a denial.

3. Mistakes with the Date of Birth (DOB)

If you enter the wrong birth date or switch them, you will fail the eligibility check right away.
Even little mistakes like:

• Reversal of month and day
  • Mistakes when typing
  • CO-31 rejections can happen if the year is wrong.

4. Changes in Insurance Coverage

Patients often switch jobs or plans without telling their doctors. If you submit a claim with old insurance information, you won’t be eligible.
This happens a lot with:

• Changes to the employer
• Renewals of Medicaid
  • Changes to Medicare plans
• Updates on COB (Coordination of Benefits)

5. Demographic information that is missing or not complete:

Payer mismatch can also happen when claims are missing information like gender, address, or subscriber relationship.

6. Mistakes in entering data or integrating systems:

Doing things by hand raises the chance of making mistakes. There may be gaps in the integration between the EHR and the billing system that cause data to be incomplete or damaged.

How CO-31 Denials Affect Income:

A CO-31 denial may seem small, but it has a big effect on operations:

Time spent by staff fixing and resubmitting claims

Reimbursements take longer

• More people getting denied
• Lowered the number of clean claims
• More days to pay accounts receivable

If not fixed, repeated eligibility mistakes can cost practices thousands of dollars every month.
That’s why it’s so important to have a structured plan for fixing eligibility denials.

How to Fix CO-31 Refusals Quick:

Taking quick action after getting a CO-31 denial will help you get your payments back faster.
Step 1: Check the patient’s information
Check again:

• • Full name as it appears on legal documents
    • ID of the member
    • Date of Birth
    • Address
    • Plan for insurance

Check against the payer portal and the insurance card.
Step 2: Check Eligibility in Real Time
Check your active coverage and correct details using payer portals or clearinghouses.
Step 3: Fix the Claim
Fix all the wrong information in the billing system and then send the claim back in with the right information.
Step 4: Send it back right away
There are deadlines for filing. Quick resubmission stops money from being lost.
Step 5: Find the root cause
Write down the reason for the denial so it doesn’t happen again. Find out if the problem came from registration, verification, or billing.

Ways to stop CO-31 denials from happening:

The best way to fix a CO-31 denial is to stop it from happening in the first place. Here are some best practices that have been shown to work:

• Checking eligibility on the front end

• • Always check insurance at: o Scheduling
    Check in
  • Before you send in your claim
  • Real-time eligibility tools cut down on mistakes by a lot.

• Digitally capture insurance cards: Scan both sides of the cards so you don’t make mistakes when entering them by hand.
• Make Registration Protocols the Same: o Use structured forms and scripts to make sure:
  • Collecting legal names
  • Correct date of birth
• Updated contact information
• Current insurance plan
• Train Staff Regularly: Staff at the front desk should know how mistakes in demographics affect sales.
• Automate Where Possible: Tools that automate tasks lower the risk of making mistakes when entering data by hand.
• Do a root cause analysis: Keep an eye on denial trends every month and find out where the same mistakes keep happening.

Denial Management Services Can Help:

Small and medium-sized practices may find it hard to handle eligibility denials on their own. To cut down on mistakes and speed up collections, many providers use specialized denial management services.
Teams of professionals:

Keep an eye on denial trends

Check to see if someone is eligible

• Fix claims more quickly
• Do a root cause analysis
• Raise the number of clean claims
• Cut down on A/R days

Healthcare organizations can avoid CO-31 denials by working with experts like Allzone Management Services Inc. These experts set up structured workflows, automated verification, and experienced billing specialists.
Their approach focuses on stopping denials before they occur—not just fixing them afterward.

In the end, every denied claim means money that could have been made sooner. But the good news is that you can stop CO-31 denials from happening with the right tools and procedures. If your company keeps having problems with eligibility, it might be time to put in place stronger controls or hire professionals who know how to stop denials from happening. A proactive strategy today can mean faster payments and healthier cash flow tomorrow.