The Top 10 Modifier Mistakes We See Every Month (And How They Cost Practices Thousands)

Small modifier. Big consequences.

Modifiers may only be two characters long, but they can determine whether a claim is paid, denied, delayed, or even audited.

Every month, we review thousands of physician claims across multiple specialties. One thing remains consistent: many denials and lost revenue opportunities come down to incorrect — or missing — modifiers.

Some modifier mistakes result in underpayments. Others trigger unnecessary audits. And many simply leave money on the table.

Here are the ten modifier mistakes we encounter most often — and how your practice can avoid them.

1. Confusing Modifier 25 and Modifier 57

This is probably the most common mistake we see. Many providers know they need "a modifier," but they aren't sure which one.

• Modifier 25 — used when a significant, separately identifiable E/M service is performed on the same day as a minor procedure (0- or 10-day global).
• Modifier 57 — used when the E/M visit results in the decision to perform a major surgery (90-day global).

The mistake: using Modifier 25 when Modifier 57 should have been reported — or vice versa.

The result:

• Claim denials
• Incorrect reimbursement
• Audit risk

2. Forgetting Modifier 24 During the Global Period

Many surgeons assume nothing can be billed during a global period. That simply isn't true.

If a patient presents with a new, unrelated condition during the post-operative period, the E/M service may be separately billable.

The mistake: billing the visit without Modifier 24 — or not billing it at all.

The result:

• Automatic denials
• Lost revenue
• Missed reimbursement opportunities

3. Using Modifier 59 When Another Modifier Is More Appropriate

Modifier 59 is often referred to as the "modifier of last resort." Unfortunately, it's frequently used to bypass edits without determining whether a more specific modifier applies.

The mistake: automatically appending Modifier 59 instead of considering the X{EPSU} modifiers (XE, XS, XP, XU) when applicable, or confirming that distinct procedural services truly exist.

The result:

• Increased audit risk
• Medical record requests
• Potential recoupments

4. Forgetting Modifier 50 for Bilateral Procedures

Some procedures are eligible for bilateral reporting. Others are not. Billing them incorrectly can significantly affect reimbursement.

The mistake: reporting two separate line items instead of Modifier 50 — or using Modifier 50 when payer policy requires RT/LT.

The result:

• Incorrect payment
• Claim rejections
• Manual review delays

5. Incorrect RT and LT Modifier Usage

Laterality matters. Some carriers require RT/LT. Others prefer units. Others require separate claim lines.

The mistake: assuming every payer processes laterality the same way.

The result:

• Denials
• Duplicate claim edits
• Delayed payment

6. Modifier 51 Applied Incorrectly

Modifier 51 identifies multiple procedures performed during the same operative session. Many billing systems automatically append it. Many providers add it manually when they shouldn't.

The mistake: adding Modifier 51 when the payer applies it automatically — or appending it to exempt procedures.

The result:

• Processing delays
• Unnecessary claim edits

7. Missing Assistant Surgeon Modifiers

When an assistant surgeon participates, the correct modifier is critical. Examples include:

• Modifier 80
• Modifier 81
• Modifier 82
• AS (when appropriate)

The mistake: forgetting the assistant modifier — or using the wrong one.

The result:

• Assistant claim denials
• Payment delays
• Appeals

8. Modifier 22 Without Supporting Documentation

Modifier 22 indicates that a procedure required substantially greater work than typically expected. It should not be used simply because a case was difficult.

The mistake: submitting Modifier 22 without:

• Operative report explanation
• Additional documentation
• Comparison to normal procedural work

The result:

• Automatic requests for records
• Delayed payment
• Denials

9. Modifier 26 and TC Confusion

Diagnostic services often contain two components: the professional interpretation and the technical component.

The mistake: billing globally when only one component was performed — or billing Modifier 26 when the practice owns the equipment and performs both components.

The result:

• Duplicate billing denials
• Overpayments
• Underpayments

10. Assuming Every Procedure Needs a Modifier

One of the biggest misconceptions in medical billing is that adding a modifier increases the likelihood of payment. It doesn't. Modifiers should only be used when documentation and payer policy support them.

The mistake: adding modifiers "just in case."

The result:

• Increased audit risk
• Unnecessary payer scrutiny
• Compliance concerns

The Bigger Problem Isn't the Modifier

One thing we've learned from auditing physician practices is this: modifier mistakes usually aren't coding problems. They're documentation and education problems.

If providers don't understand why a modifier is necessary — or if documentation doesn't support it — the claim becomes vulnerable.

The modifier is simply the symptom. The underlying issue is often workflow, documentation, or a lack of specialty-specific education.

Five Questions Every Practice Should Ask

Before appending any modifier, ask:

• Does the documentation support it?
• Is it required by this payer?
• Is there a more specific modifier available?
• Does it change reimbursement appropriately?
• Would the claim make sense if it were audited six months from now?

If the answer to any of these questions is "no," it's time to take another look.

The Bottom Line

Modifiers aren't shortcuts to payment. They're communication tools that tell the payer why a service deserves separate consideration.

When used correctly, they help ensure physicians are reimbursed accurately for the care they provide. When used incorrectly, they can create denials, payment delays, compliance issues, and unnecessary administrative work.

The most successful physician groups don't use more modifiers than everyone else. They use the right modifier, for the right reason, backed by the right documentation.

Because in today's reimbursement environment, two small characters can make a very big difference.