Modifier 23 in Medical Billing: When and How to Use It

Modifier 23 means “Unusual Anesthesia.” It’s appended to a surgical procedure code to indicate that anesthesia services were more extensive than typically expected due to unusual circumstances.

CPT Definition:

Modifier 23 – Unusual Anesthesia: “When a procedure which usually requires either no anesthesia or local anesthesia must be done under general anesthesia due to unusual circumstances.”

Translation:

Let’s say you’re billing for a minor procedure (like a colonoscopy or cardiac cath) that normally doesn’t require general anesthesia. But for this particular case, maybe due to patient anxiety, severe pain, or an underlying condition, general anesthesia was necessary. That’s when Modifier 23 enters the scene.

Table of Contents

When Should You Use the 23 Modifier?

Here are the most common scenarios that justify the use of Modifier 23:

Pediatric or geriatric patients requiring general anesthesia for minor procedures
Patients with developmental delays, extreme anxiety, or mental health conditions
Cases where local anesthesia failed, and general anesthesia became necessary
Medical complications like cardiac instability or severe comorbidities
Procedures on non-compliant or unresponsive patients

✅ Tip: Always make sure the reason for unusual anesthesia is clearly documented in the medical record.

How to Document the 23 Modifier Correctly

Poor documentation is a fast track to denials. Here’s what you must include in the patient’s chart to support Modifier 23:

Reason for using general anesthesia instead of the usual method
Clinical notes showing why local or no anesthesia was insufficient
Anesthesiologist’s report detailing the type and duration of anesthesia
Pre-op evaluation identifying any special considerations or complications

Example: “Procedure performed under general anesthesia due to severe autism spectrum disorder with non-verbal, combative behavior. Local anesthesia not feasible.”

Best Practices for Applying the 23 Modifier in Medical Billing

Here are best practices to ensure clean claims and maximum reimbursement:

Attach it to the surgical CPT code, not the anesthesia code.
Do not use Modifier 23 routinely. It flags unusual cases — overuse may trigger audits.
Always include strong documentation from both surgeon and anesthesiologist.
Pre-authorize when possible (especially for elective or outpatient procedures).
Appeal denials with detailed records and explain why general anesthesia was medically necessary.

Common Mistakes with the 23 Modifier (And How to Avoid Them)

Even seasoned coders can get tripped up. Watch out for these:

Mistake	Why It’s a Problem	How to Fix It
Using 23 with the anesthesia CPT	Incorrect code pairing	Always append it to the surgical CPT
No documentation	Leads to denial or audit	Document everything thoroughly
Misuse on routine cases	Seen as upcoding	Use only when truly warranted
Using with inpatient-only procedures	Usually not appropriate	Confirm if the procedure is eligible

Comparison: 23 Modifier vs 24 & 25 Modifiers

Confused between 23, 24, and 25? Here’s a quick comparison:

Modifier	Purpose	Used With	Example
23	Unusual anesthesia	Surgical codes	Patient required general anesthesia for a minor procedure
24	Unrelated E/M service during post-op	E/M codes	Follow-up visit for new issue after surgery
25	Significant, separately identifiable E/M on same day	E/M codes	Separate office visit from procedure

How to Maximize Reimbursement with the 23 Modifier

To get paid correctly (and fast), follow this mini-strategy:

Check payer guidelines — some require extra forms or documentation for 23
Pair with correct surgical CPT — double-check code specificity
File with complete operative and anesthesia notes
Use appeals when denied — many payers initially deny 23 claims that are later approved on resubmission

Alternatives to the 23 Modifier in Medical Billing

Modifier 23 has a very specific use case, but if it doesn’t apply, consider these alternatives:

Modifier 22 (Increased Procedural Services): For more complex or time-consuming procedures
Modifier 53 (Discontinued Procedure): If a procedure was started but not completed due to patient status
Anesthesia-specific modifiers (AA, QX, QS, etc.): When documenting provider roles or monitored anesthesia care

Note: Don’t confuse anesthesia billing modifiers (like QS, QK, QY) with Modifier 23, which reflects the nature of the procedure — not who provided the anesthesia.

Impact of the 23 Modifier on Medical Billing Processes

While rare, Modifier 23 can significantly impact your billing workflow:

Increased reimbursement: Since general anesthesia often increases complexity and costs
Longer adjudication times: Some payers require manual review
Audit triggers: Due to its “unusual” classification, it can attract payer attention

That’s why using it wisely and defensibly is critical for both compliance and revenue.

Final Takeaways: What Every Medical Biller Should Know

✅ Use Modifier 23 only when general anesthesia is medically necessary for a typically low-anesthesia procedure
✅ Ensure clear, detailed documentation supports the need
✅ Know payer-specific rules and prepare for potential scrutiny
✅ Train staff and clinicians on when and how to flag cases for Modifier 23

23 Modifier In Medical Billing