Understanding Claim Response Codes: A3 and 91

When the Claim Can't Move Forward

A rejected claim is frustrating enough. But when it's stopped before it ever reaches adjudication, it can feel like the system is working against you. That's exactly what happens with the A3 and 91 combination, one of the most common eligibility-related rejections in medical billing.

Together, these codes mean the claim was returned before processing because an entity associated with the claim wasn't eligible or approved for the dates of service billed. The payer didn't review it, deny it or pend it. It simply couldn't accept it.

Understanding why this happens, and what to do about it, can save your team significant time and help protect your cash flow.

Quick Definitions

Before we talk about fixing the problem, let's break down what these codes mean.

A3 — Acknowledgement/Claim returned as unprocessable. The claim was rejected and not entered into the adjudication system.

91 — Entity not eligible or not approved for dates of service. This code requires the use of an entity code to identify which party triggered the issue. In this combination, the entity is unspecified, which means the response requires closer review to determine the source of the problem.

Put together, these codes signal that something about the patient's coverage, the provider's network status or the service itself didn't align with what the payer has on file for those specific dates.

These codes often appear together in claim responses, but they do not always represent a fixed or official pairing.

Why You're Seeing It

This rejection occurs when the payer can't confirm eligibility or approval for the dates of service on the claim. Because the entity isn't specified in this response, the issue could trace back to several places.

Common causes include:

• The patient's insurance coverage was inactive or lapsed on the date of service.
• The provider wasn't in-network or wasn't credentialed to bill during the claim period.
• The service or procedure isn't covered under the patient's plan for those specific dates.
• Insurance information in the patient's record was outdated or entered incorrectly.
• A coverage gap exists between plan terms that wasn't identified before the visit.

In many cases, this rejection is preventable. The claim was submitted with information that appeared correct in your system but didn't match what the payer had on record.

How to Fix It

Start by pulling the payer or clearinghouse response to identify which date range or entity is flagged. Then work through these steps:

• Verify the patient's insurance was active on the date of service by running a real-time eligibility check.
• Confirm the provider's network status and credentialing dates with the payer.
• Review the patient's plan benefits to confirm coverage for the specific service billed.
• Cross-check the claim's relevant form fields. For HCFA claims, review fields 1a, 2, 3 and 4. These carry the patient and insured information that payers use for eligibility validation.
• Update any incorrect or outdated insurance information in your system before resubmitting.

Once you've identified and corrected the issue, resubmit the claim with updated data. Don't resubmit without making a change. The payer will return the same response.

How to Prevent It Next Time

Most A3 and 91 rejections can be avoided by building eligibility verification into your standard workflow, before the patient is ever seen.

• Verify eligibility and benefits in real time for every patient before the visit. Don't rely on what was confirmed at a prior appointment.
• Check provider network status and approval dates at the start of each plan year and any time a payer updates their directory.
• Keep patient insurance information current in your practice management system. Patients change plans, employers and coverage tiers more often than you'd expect.
• Train your front desk team to flag discrepancies between the insurance card on file and what the payer returns in the eligibility response.
• For services that require prior authorization or payer-specific approval, confirm that authorization covers the exact dates of service before the claim is submitted.

Routine eligibility checks are the single most effective way to reduce this type of rejection.

Related Codes You Might See

If you're seeing A3 and 91 in your responses, these codes sometimes appear nearby when coverage or eligibility issues are present:

CO-4 — The service/procedure/revenue code is inconsistent with the modifier.

CO-27 — Expenses incurred after coverage terminated.

PR-96 — Non-covered charge(s).

If multiple codes appear together, the claim may have both an eligibility issue and a coverage or billing mismatch that needs to be resolved before resubmission.

Real-World Example

A billing team submits a claim for a patient who switched insurance plans at the start of the year. The old plan ID was still in the system, so the claim went out with coverage that had already ended. The payer returned it with A3 and 91. After pulling an updated eligibility response with the correct plan, the team corrected the insurance information, updated the claim and resubmitted successfully.

Before You Resubmit, Make Sure You Do These Things

• Run a real-time eligibility check for the correct date of service.
• Confirm the provider's credentialing and network status with the payer.
• Update patient insurance details if anything has changed.
• Verify that the service billed is covered under the patient's active plan.
• Review HCFA fields 1a, 2, 3 and 4 for accuracy before resubmitting.

Want to catch eligibility issues before they become rejections? Service Center by Office Ally® supports real-time eligibility and benefits verification so you can confirm patient coverage before the visit, not after the claim comes back. Want to talk to someone about how Service Center and Office Ally's suite of solutions can improve your workflow? Contact our sales team today and find out how we can help.

‍This blog was generated with the assistance of artificial intelligence (AI) and reviewed by
Office Ally's subject-matter experts for accuracy. It is intended for informational purposes only and does not constitute medical, legal or billing advice.