CPT Code 31231: Diagnostic Nasal Endoscopy Billing Guide for ENT Practices in 2026

What Is CPT Code 31231?

CPT code 31231 is the procedure code for diagnostic nasal endoscopy, unilateral or bilateral, designated as a separate procedure. It covers the insertion of a rigid or flexible nasal endoscope to examine the nasal cavity, meatus, turbinates, and sinonasal anatomy beyond what anterior rhinoscopy can visualize. It is one of the highest-volume diagnostic codes in ENT practice and carries specific bundling rules that directly affect reimbursement.

Quick Answers

It is a “separate procedure”: The separate procedure designation means 31231 is considered part of the work when a more comprehensive surgical endoscopy code is performed in the same session. It can only be billed independently when no other nasal or sinus endoscopy procedure is performed during the same encounter.

Medicare reimburses approximately $193 in office settings: The 2026 national average Medicare non-facility reimbursement for 31231 is approximately $193.39, based on 5.79 total RVUs and the $33.40 conversion factor. It carries a 0-day global period, meaning there is no post-operative care window built into the payment.

Bundling is the primary billing issue: 31231 bundles into every surgical nasal endoscopy code (31233 through 31298). When a surgical sinus procedure follows the diagnostic endoscopy in the same session, only the surgical code is reported. Billing both is an unbundling violation.

What Does “Separate Procedure” Mean for 31231?

The “separate procedure” designation in the CPT code descriptor for 31231 is the single most important billing concept for this code. It means that diagnostic nasal endoscopy is considered an integral part of a more comprehensive endoscopic procedure when both are performed in the same operative session. If a surgeon performs a diagnostic nasal endoscopy and then proceeds to endoscopic sinus surgery in the same encounter, the diagnostic component is bundled into the surgical code, and 31231 is not reported separately.

31231 is only reportable when it is the only endoscopic procedure performed during the encounter, or when it is performed for a clinically distinct reason from the surgical procedure and documentation supports a separate indication. In the second scenario, modifier 59 or XS (separate structure or separate encounter) is required to override the NCCI bundling edit, and the documentation must clearly establish why the diagnostic endoscopy was a distinct service from the surgical procedure.

One question we hear constantly from ENT practice managers is why their diagnostic nasal endoscopy claims keep getting denied when the procedure was clearly performed. The answer is almost always the separate procedure rule: the claim included 31231 alongside a surgical nasal endoscopy code, and the payer correctly identified it as a bundling violation. Understanding this rule prevents the denial before it happens. For a similar diagnostic code with its own bundling rules, see our guide to CPT 31575 for flexible laryngoscopy. The same principle applies: diagnostic codes bundle into surgical codes when both are performed in the same session.

Is CPT 31231 a Surgical Procedure?

No. CPT 31231 is classified as a diagnostic procedure despite appearing in the Surgery section of the CPT manual. The code descriptor explicitly states “diagnostic,” meaning it covers only visualization, examination, and assessment of the nasal cavity and sinonasal structures. It does not include any therapeutic intervention such as biopsy, polypectomy, tissue removal, or debridement.

This distinction matters for billing because 31231 carries a 0-day global period (indicator 000), meaning there is no post-operative care window included in the reimbursement. A same-day E/M service is generally considered part of the procedure’s pre-operative assessment, but office visits on subsequent days for unrelated care are separately billable without restriction. Surgical nasal endoscopy codes (31233 through 31298) carry their own global periods and different payment rules.

Across the billing companies we vet for ENT practices, a recurring confusion is whether 31231 should be treated as a “minor procedure” for modifier 25 purposes. The answer is yes: 31231 has a 0-day global period, which means it qualifies as a minor procedure under CMS rules. When a separately identifiable E/M visit is documented on the same day, modifier 25 is appended to the E/M code. The same modifier 25 documentation standard that applies to flexible laryngoscopy (31575) applies here.

How Does 31231 Bundle with Other Codes?

CPT 31231 is the base code for the nasal endoscopy family. When any surgical nasal endoscopy code is reported on the same date of service, 31231 is considered included in the surgical code’s work and cannot be billed separately. This applies to every code in the 31233 through 31298 range.

CPT Code	Description	Bundles with 31231?
31233	Nasal endoscopy with maxillary sinusoscopy	Yes, 31231 is included
31237	Nasal endoscopy with biopsy/polypectomy	Yes, 31231 is included
31254	Nasal endoscopy with ethmoidectomy, partial	Yes, 31231 is included
31256	Nasal endoscopy with maxillary antrostomy	Yes, 31231 is included
31267	Nasal endoscopy with frontal sinus exploration	Yes, 31231 is included
31575	Flexible laryngoscopy, diagnostic	Does not bundle; different anatomic scope

The one exception in the table above is CPT 31575 (flexible laryngoscopy). Because 31575 examines the larynx and 31231 examines the nasal cavity, they address different anatomic structures and are not bundled under NCCI edits by default. Both can be billed on the same date when the documentation supports separate clinical indications for each procedure. Modifier 59 or XS is appended to the secondary code to indicate distinct services.

In our experience matching ENT providers with billing partners, the most common 31231 bundling error is not the obvious one (billing it with sinus surgery), but the subtle one: billing 31231 and 31575 together without documenting separate indications for each scope. A single chief complaint of “nasal congestion” used to justify both a nasal endoscopy and a laryngoscopy invites payer scrutiny, even though the codes do not technically bundle. Each procedure needs its own documented clinical rationale.

What Documentation Does 31231 Require?

Complete documentation for a 31231 claim must demonstrate the clinical indication, the scope of the examination, and the findings. Missing any element gives the payer grounds for denial or recoupment.

Indication for the procedure: Document the clinical reason anterior rhinoscopy was insufficient and endoscopic visualization was required. Common indications include chronic sinusitis, nasal polyps, epistaxis, nasal obstruction, septal deviation evaluation, and post-surgical surveillance.

Scope type: Specify whether a rigid or flexible nasal endoscope was used. CPT 31231 covers both, but the type should be documented.

Structures visualized: Record which structures were examined: inferior turbinate, middle turbinate, middle meatus, sphenoethmoidal recess, nasopharynx, and any sinus ostia visualized. Document findings for both sides if performed bilaterally.

Findings: Document all normal and abnormal findings, including mucosal edema, purulence, polyps, crusting, anatomic variants, or post-surgical changes.

Clinical interpretation: Include a diagnostic impression signed by the examining provider.

Separate indication (if billing with another procedure): If 31231 is billed on the same day as another endoscopic procedure with modifier 59 or XS, the documentation must clearly establish why the diagnostic endoscopy was a distinct service with its own clinical justification.

For practices that also perform tympanostomy tubes under CPT 69436 or comprehensive audiometry under CPT 92557, the documentation principle is identical: every element the code requires must appear in the note.

Common 31231 Denials and Fixes

Diagnostic nasal endoscopy generates a predictable set of denials. Each one has a process-level fix that prevents recurrence.

Unbundling with surgical endoscopy. Billing 31231 alongside a surgical nasal endoscopy code (31233 through 31298) when the diagnostic component is already included. Fix: report only the surgical code when both are performed in the same session.

Modifier 59 without supporting documentation. Appending modifier 59 to override the NCCI edit but the note does not document a distinct clinical indication for the diagnostic endoscopy. Fix: document separate indications before appending the modifier.

Insufficient documentation of medical necessity. The note does not explain why endoscopic visualization was needed beyond what anterior rhinoscopy could provide. Fix: document the specific limitation of anterior rhinoscopy and the clinical question the endoscopy was performed to answer.

Frequency limits. Some payers impose frequency limits on diagnostic nasal endoscopy, especially for serial follow-up in chronic conditions. Fix: check payer-specific frequency policies and ensure each encounter documents a clinical change that justifies a repeat procedure.

Missing diagnosis code specificity. Using J32.9 (chronic sinusitis, unspecified) when a site-specific code like J32.0 (chronic maxillary sinusitis) is documented in the note. Fix: code to the highest specificity supported by the documentation.

Same-day E/M overbilling. Billing a same-day E/M visit with modifier 25 when the documentation does not support a separately identifiable evaluation. Fix: verify that the E/M note documents distinct clinical work beyond the pre-procedure assessment for the endoscopy.

Providers often come to us after watching their nasal endoscopy denial rate climb and discovering that the denials trace back to one of these six patterns repeated across dozens of claims. The fix is not more coding knowledge. It is a billing workflow that catches the error before the claim is submitted.

Frequently Asked Questions

Next Steps

Need to review related ENT procedure codes? See our guides to CPT 31575 for flexible laryngoscopy, CPT 69436 for tympanostomy tube placement, and CPT 92557 for comprehensive audiometry.

For a broader overview of ENT coding, start with our ENT CPT and ICD-10 codes guide.

To learn how ENT Billing Services connects providers with billing partners, visit our About Us page.