CPT code 00164 describes anesthesia services provided to a patient undergoing a soft tissue biopsy of the nose and accessory sinuses. It falls within the anesthesia code family for procedures on the head (CPT 00100–00222) and is assigned 5 base units by the American Society of Anesthesiologists (ASA) Relative Value Guide. This code is reported by the anesthesiologist or CRNA — not the surgeon — and is never used to represent the biopsy procedure itself. Understanding when 00164 applies, how it computes into a reimbursable claim, and how it differs from adjacent nose-and-sinus anesthesia codes is essential for any ENT or otolaryngology revenue cycle team.
What Does CPT Code 00164 Mean?
CPT 00164 is the correct anesthesia procedure code when a provider administers anesthesia — whether general, regional, or monitored anesthesia care (MAC) — specifically for a soft tissue biopsy of the nose or accessory sinuses. The code is maintained by the American Medical Association CPT Editorial Panel within the anesthesia section of the CPT code set and is classified under “Anesthesia for Procedures on the Head.”
Key attributes at a glance:
- Code type: Anesthesia (CPT 00100–01999 range)
- ASA base units: 5
- Applicable setting: Hospital inpatient, hospital outpatient, ambulatory surgical center (ASC)
- Provider type: Anesthesiologist (MD/DO), CRNA, or anesthesiologist assistant (AA) under appropriate supervision
- Service category: Head/nose and accessory sinuses — soft tissue biopsy only
- Surgical crosswalk: Typically paired with the surgeon’s CPT code 30100 (Biopsy, intranasal) or 31237 (Nasal/sinus endoscopy with biopsy) on the claim
What Procedures Does CPT 00164 Cover?
CPT 00164 covers the anesthesia management component of soft tissue biopsy procedures involving the nasal cavity and accessory sinuses, which include the maxillary, ethmoid, frontal, and sphenoid sinuses. The code encompasses the full scope of anesthesia care — pre-induction assessment, intraoperative monitoring, and immediate post-procedure handoff — rather than any specific anesthetic technique.
Clinical presentations typically supported by this code:
- Unexplained nasal mass or polypoid tissue requiring histologic diagnosis
- Suspected intranasal neoplasm (benign or malignant)
- Chronic granulomatous disease workup (e.g., sarcoidosis, Wegener’s/GPA, fungal sinusitis)
- Recurrent or refractory nasal lesion with malignancy concern
- Tissue sampling from accessory sinus mucosa during ENT evaluation
- Pediatric patients in whom the complexity or anxiety level makes general anesthesia medically necessary for a nasal biopsy
What Does CPT 00164 Specifically Exclude?
CPT 00164 does not cover:
- Anesthesia for surgical excision or destruction of nasal lesions (these may warrant 00160 or a more specific code depending on the procedure)
- Anesthesia for radical nasal/sinus surgery — use CPT 00162 (7 base units)
- The biopsy procedure itself — that is reported separately by the surgeon
- Local anesthesia administered by the surgeon without an anesthesiologist or CRNA present (no separate anesthesia claim is appropriate)
- Anesthesia for nasal endoscopy performed purely for diagnostic visualization without tissue sampling — that scenario more closely maps to 00160
When Is CPT 00164 the Right Code to Use?
Selecting 00164 correctly requires matching two conditions simultaneously: the correct anatomic site and the correct procedure type. In practice, anesthesia coders must verify both elements from the anesthesia record and the surgeon’s operative note before submitting the claim.
Follow this selection sequence:
- Confirm the anatomic location — The procedure must involve the nose (nasal cavity) or an accessory sinus, not the nasopharynx, oral cavity, or trachea.
- Confirm the procedure type — The surgical CPT assigned by the surgeon must be a biopsy (e.g., 30100 or 31237), not a polypectomy-only, septoplasty, or other therapeutic intervention.
- Confirm anesthesia was separately provided — An anesthesiologist, CRNA, or AA must have been present and managing anesthesia independently.
- Confirm the biopsy involved soft tissue — Hard tissue or bone involvement may redirect you to a different code family entirely.
- Verify no more complex procedure was performed concurrently — If the surgeon also performed sinus surgery during the same session, the anesthesia code for the most complex procedure governs; 00162 or 00160 may apply instead.
How Does CPT 00164 Differ From CPT 00160?
This is the most common coding decision point in ENT anesthesia billing. Both codes apply to the nose and accessory sinuses, but the procedure type determines which is correct.
| Feature | CPT 00160 | CPT 00164 |
|---|---|---|
| Full descriptor | Anesthesia for procedures on nose and accessory sinuses; not otherwise specified | Anesthesia for procedures on nose and accessory sinuses; biopsy, soft tissue |
| Base units (ASA) | 5 | 5 |
| Use when | Procedure doesn’t fit a more specific code in this family | Procedure is specifically a soft tissue biopsy |
| Common surgical crosswalk | Diagnostic endoscopy (no biopsy), turbinate procedures | CPT 30100, CPT 31237 with biopsy |
| Specificity | Catch-all / NOS | Procedure-specific |
In practice, when the surgeon’s operative note documents a tissue sample taken for pathologic analysis, 00164 is the more specific and appropriate choice over 00160, even though their base unit values are identical.
What Documentation Is Required to Support CPT 00164?
Because anesthesia billing and coding is time-based and tied to a surgical procedure performed by a separate provider, the documentation supporting 00164 must come from multiple sources.
What Must the Anesthesia Provider Document?
A complete anesthesia record supporting CPT 00164 must include:
- Pre-anesthesia evaluation — Documented ASA physical status classification (P1–P6), relevant medical history, medication review, airway assessment, and anesthesia plan
- Anesthesia start time — The precise time the anesthesiologist or CRNA began preparing the patient for induction (not the surgical start time)
- Anesthesia type administered — General endotracheal anesthesia, laryngeal mask airway (LMA), or MAC must be documented along with agents used
- Continuous intraoperative monitoring — Documentation of vital signs, oxygen saturation, and the provider’s continuous presence or medical direction
- Anesthesia stop time — The time the provider transferred care to post-anesthesia recovery (PACU) personnel
- Total anesthesia time in minutes — Used to calculate time units; every 15 minutes equals one time unit under Medicare and most payers
- Physical status modifier — ASA P1 through P6 must be assigned and documented in the anesthesia record
- Qualifying circumstances (if applicable) — If extreme age, emergency, or controlled hypotension applies, supporting add-on codes (99100, 99116, 99135, 99140) require documentation of the specific circumstance
How Do Anesthesia Payment Rules Apply Differently From E&M or Surgical Codes?
CPT 00164, like all anesthesia codes, does not use the standard RBRVS physician RVU formula. Instead, reimbursement follows the Standard Anesthesia Formula:
(Base Units + Time Units + Physical Status Units*) × Anesthesia Conversion Factor = Allowable Payment
*Physical status units are recognized by most commercial payers but not by Medicare.
What Are the Documentation Standards for Facility vs. Non-Facility Settings?
| Documentation Element | Facility (Hospital/ASC) | Non-Facility (Office — Rare) |
|---|---|---|
| Anesthesia record | Required in medical record | Required; provider retains copy |
| Pre-op evaluation note | Inpatient H&P or pre-op note | Separate pre-anesthesia assessment note |
| Surgeon’s operative note | Filed in chart; anesthesia coder must review | Must be obtained before claim submission |
| PACU/recovery documentation | Standard inpatient/outpatient protocol | Transfer of care note required |
How Does CPT 00164 Affect Medical Billing and Reimbursement?
Anesthesia reimbursement for CPT 00164 does not work like a standard physician fee schedule code. Payment is computed using the anesthesia formula rather than an RVU-to-conversion-factor calculation. The 5 base units assigned to 00164 reflect the moderate — though not complex — nature of nasal biopsy anesthesia management.
CPT 00164 Anesthesia Payment Calculation Framework
| Component | Value | Notes |
|---|---|---|
| ASA Base Units | 5 | Fixed; does not change with payer or year |
| Time Units | Variable | 1 unit per 15 minutes (Medicare); some commercial payers round up |
| Physical Status Units (commercial) | 0–5 added | P1=0, P2=0, P3=1, P4=2, P5=3; not recognized by Medicare |
| Qualifying Circumstances Units | +2 to +5 | Add-on codes 99100–99140 if applicable |
| Medicare Anesthesia CF (2025) | $20.3178 | National rate; adjusted by GPCI for locality |
| Example: 30-min procedure, P2 patient | (5 + 2) × $20.3178 = ~$142.22 | Medicare estimate; commercial rates substantially higher |
The 2025 Medicare Anesthesia Conversion Factor is $20.3178, reflecting a 2.20% decrease from the 2024 figure of $20.7739. ASA Commercial payers negotiate their own conversion factors independently; the median commercial anesthesia conversion factor has historically been three to four times higher than Medicare’s rate.
Additional billing considerations:
- Claims must be submitted on the CMS-1500 form (or electronic equivalent) with the appropriate anesthesia provider modifier
- Total anesthesia time in minutes must appear in box 24G; Medicare computes time units to one decimal place
- The surgical CPT code (e.g., 30100) should appear on the surgeon’s separate claim — not on the anesthesia claim
What Modifiers Are Commonly Used With CPT 00164?
| Modifier | Description | When to Apply | Billing Impact |
|---|---|---|---|
| AA | Anesthesia personally performed by anesthesiologist | Solo physician-only case | Full allowable |
| QZ | CRNA service without medical direction | Independent CRNA | Full allowable to CRNA |
| QX | CRNA under medical direction of anesthesiologist | Team model (CRNA + physician) | Split payment |
| QK | Medical direction of 2–4 CRNAs by anesthesiologist | Concurrent supervision | Reduced physician rate |
| AD | Medical supervision of 5+ concurrent procedures | Exceeds QK threshold | Per-case limit applies |
| QS | MAC services | MAC case | Indicates monitoring anesthesia only |
| P1–P6 | Physical status modifiers | Always append | Affects commercial payment; informational for Medicare |
| 23 | Unusual anesthesia | General anesthesia required for ordinarily local-only procedure | Requires documentation of medical necessity |
Modifier 23 deserves particular attention for CPT 00164. Nasal biopsies are frequently performed under local anesthesia in an office setting. When an anesthesiologist is called to provide general anesthesia or MAC for what would ordinarily be a local-only procedure, modifier 23 (Unusual Anesthesia) must be appended and the anesthesia record must document the specific medical reason general or MAC anesthesia was medically necessary — such as severe anxiety disorder, uncooperative pediatric patient, or significant comorbidity.
Are There Any Prior Authorization, Coverage Restrictions, or LCD Requirements?
- Medicare: No published NCD specific to CPT 00164; coverage follows general medical necessity standards. Anesthesia is covered when the underlying surgical procedure (biopsy) is medically necessary and when the complexity or patient condition requires anesthesia management beyond local administration by the surgeon.
- Medical necessity documentation: The clinical indication for the biopsy (ICD-10 diagnosis code) drives coverage; commonly paired diagnoses include J34.1 (nasal polyp), D14.0 (benign neoplasm of nose/nasal cavity), C30.0 (malignant neoplasm of nasal cavity), and J34.89 (other disorders of nose/sinuses).
- Modifier 23 claims: Expect enhanced scrutiny; payers may request clinical documentation confirming why general/MAC anesthesia was required rather than local infiltration by the surgeon.
- NCCI edits: No known Column 1/Column 2 edit pairs that would bundle 00164 with the surgeon’s biopsy code, as they are reported on separate claims by separate providers.
What CPT or HCPCS Codes Are Commonly Billed Alongside CPT 00164?
The anesthesia claim (00164) and the surgeon’s claim are submitted separately, but both must align in terms of date of service, facility, and clinical documentation. The following codes frequently appear in the same patient encounter.
| Associated Code | Description | Typical Pairing Context | Bundling Risk |
|---|---|---|---|
| 30100 | Biopsy, intranasal | Surgeon’s primary procedure code; direct crosswalk to 00164 | No (separate claims) |
| 31237 | Nasal/sinus endoscopy with biopsy, polypectomy, or debridement | Endoscopic approach to biopsy | No (separate claims) |
| 99100 | Qualifying circumstance — extreme age | Pediatric or very elderly patient | Add-on only; do not bill standalone |
| 99140 | Qualifying circumstance — emergency conditions | Emergency biopsy scenario | Add-on only |
| 88305 | Level IV surgical pathology | Pathologist’s examination of biopsy specimen | Reported by pathologist; no bundling conflict |
| 00160 | Anesthesia, nose/sinus NOS | May be used if biopsy is incidental to broader procedure | Do not report with 00164 same date/provider |
Which Code Combinations Trigger NCCI or CCI Edits?
- Reporting both 00160 and 00164 for the same anesthesia episode by the same provider on the same date is incorrect and will be denied. Only one anesthesia code may be reported per anesthetic for a given procedure session.
- Reporting qualifying circumstance codes (99100, 99116, 99135, 99140) as standalone codes without a primary anesthesia code will result in claim rejection — these are add-on codes only.
- Reporting the surgeon’s procedure code (30100) on the anesthesiologist’s claim is a crossover billing error; each provider bills their own role separately.
What Coding Errors Should You Avoid With CPT 00164?
In practice, anesthesia billing for ENT nasal procedures generates a predictable cluster of claim errors. The following are ranked by audit frequency and compliance risk:
- Reporting 00160 instead of 00164 — When the operative note confirms a tissue biopsy was taken, 00164 is the specific code; defaulting to the NOS code (00160) is technically acceptable but loses the claim’s precision, which can trigger consistency edits on high-volume claims.
- Omitting modifier 23 when local anesthesia would normally suffice — Without modifier 23 and supporting documentation, payers may deny the anesthesia claim entirely, arguing the service was the surgeon’s responsibility.
- Incorrect time unit computation — Billing 60 minutes as 4.0 units (rather than 4.0 under Medicare’s one-decimal rule) or rounding up to 5 per commercial payer convention without verifying the contract creates systematic underpayment or overpayment.
- Appending physical status modifiers to Medicare claims without understanding their informational-only status — Medicare does not add payment for P3–P5 modifiers; commercial payers do. Misapplying commercial billing logic to Medicare creates inconsistency in expected reimbursement.
- Billing qualifying circumstance codes without documentation — Add-on codes 99100 (extreme age) and 99140 (emergency) will not survive audit if the anesthesia record does not explicitly state why the qualifying circumstance applied.
- Using 00164 when a more complex concurrent nasal/sinus procedure was performed — If the surgeon documents both a biopsy and a functional endoscopic sinus surgery (FESS) in the same session, the anesthesia code for the most resource-intensive procedure governs the claim.
What Do Auditors and RAC Reviewers Look for When Reviewing Claims With CPT 00164?
- Time unit accuracy: Anesthesia start and stop times in the anesthesia record must mathematically support the time units billed.
- Modifier 23 justification: Any claim with modifier 23 appended is a higher-scrutiny target; reviewers will request the full anesthesia record and pre-op evaluation note.
- Medical necessity for anesthesia beyond local: Payers assess whether the patient’s documented comorbidities or the procedure’s complexity genuinely required anesthesia management separate from the surgeon’s local infiltration.
- Concurrent billing patterns: Anesthesiologists billing QK modifier (directing 2–4 CRNAs) must have documentation confirming compliance with the seven core medical direction requirements per CMS Medicare Claims Processing Manual, Chapter 12, Section 50.
How Does CPT 00164 Relate to Other CPT Codes?
Understanding 00164’s position within the anesthesia nose-and-sinus code family prevents both upcoding (moving to a higher-base-unit code without justification) and undercoding (defaulting to NOS when a specific code exists).
| Related Code | Relationship Type | Base Units | Key Distinction |
|---|---|---|---|
| 00160 | Same family — NOS | 5 | Use when no more specific code fits; 00164 is preferred for biopsy |
| 00162 | Same family — radical surgery | 7 | Reserved for radical nasal/sinus surgery; higher complexity |
| 00164 | This code — biopsy, soft tissue | 5 | Specific to soft tissue biopsy only |
| 00170 | Adjacent family — intraoral | 5 | Mouth and oral cavity; not for nasal procedures |
| 00190 | Head — facial bones/skull | 5 | Facial bone procedures, not soft tissue nasal biopsy |
| 30100 | Surgical crosswalk (surgeon code) | N/A | Intranasal biopsy; the procedure code on the surgeon’s claim |
| 31237 | Surgical crosswalk (surgeon code) | N/A | Endoscopic nasal/sinus biopsy; may crosswalk to 00164 |
What Is the Correct Code Sequencing or Reporting Order When CPT 00164 Appears With Other Codes?
- Primary anesthesia code (00164): Always appears first on the anesthesia claim.
- Physical status modifier (P1–P6): Appended directly to 00164 on the same claim line.
- Provider role modifier (AA, QZ, QX, QK, AD): Appended after physical status modifier.
- QS modifier (if MAC): Appended if monitored anesthesia care was provided rather than general anesthesia.
- Qualifying circumstance add-on codes (99100, 99116, 99135, 99140): Reported on a separate line below the primary anesthesia code, never as standalone.
- Separately billable services (e.g., arterial line placement, TEE): Reported on additional claim lines with their own CPT codes; these are not bundled into the 00164 base units per ASA Relative Value Guide guidelines.
Real-World Coding Scenario — How CPT 00164 Is Applied in Practice
A 58-year-old patient with a history of sarcoidosis and a new right nasal mass presents for an intranasal biopsy. Due to poorly controlled hypertension and significant anxiety, the ENT surgeon requests anesthesia support. The anesthesiologist performs a pre-operative evaluation, assigns an ASA P3 physical status, and provides general anesthesia via LMA. The procedure lasts 34 minutes. The anesthesiologist documents anesthesia start at 9:04 AM and anesthesia stop at 9:38 AM (34 minutes = 2.27 time units, rounded to 2.3 for Medicare). The surgeon’s operative note documents a biopsy of a soft tissue lesion of the right nasal cavity using forceps; no additional sinus procedures were performed.
Correct Code Application
- Anesthesia claim: CPT 00164-P3-AA
- Qualifying circumstance: Not applicable (this is not extreme age or emergency)
- Time: 34 minutes = 2.3 time units (Medicare)
- Calculation (Medicare estimate): (5 + 2.3) × $20.3178 = ~$148.32 allowable
- Surgeon’s claim (separate): CPT 30100 with appropriate diagnosis code (e.g., D14.0)
Common Mistake in This Scenario
- Incorrect: Billing CPT 00160 (NOS) because the coder did not review the surgeon’s operative note confirming a biopsy — a documentation review lapse that defaults to the generic code.
- Why it fails: While 00160 and 00164 carry the same base units, using the NOS code when a specific code exists reflects incomplete coding practice and can trigger consistency flags if 00164 appears on the surgeon’s claim-supporting documentation but 00160 appears on the anesthesia claim.
- Also incorrect: Appending modifier 23 without documentation of medical necessity for anesthesia — this modifier requires a written justification in the anesthesia record explaining why local-only anesthesia was inadequate for this specific patient.
Frequently Asked Questions About CPT Code 00164
Is CPT Code 00164 Still Valid for Use in 2026?
CPT code 00164 remains a valid, active anesthesia procedure code for 2026 with no changes to its descriptor or base unit value. CMS has confirmed that anesthesia base units are unchanged for CY 2026 CMS, meaning the 5-unit assignment for 00164 carries forward without modification. Coders should verify the current conversion factor for their Medicare locality, as the anesthesia conversion factor does adjust annually.
What Is the Difference Between CPT 00164 and CPT 00160?
CPT 00164 is the procedure-specific anesthesia code for a soft tissue biopsy of the nose or accessory sinuses, while CPT 00160 is the not-otherwise-specified (NOS) catch-all for nasal and sinus procedures that don’t fit a more defined code. Both carry 5 ASA base units, so the reimbursement is identical — but 00164 is more specific and should always be used when the documented procedure is a soft tissue biopsy.
What Modifier Does an Independent CRNA Use When Billing CPT 00164?
An independent CRNA who provides anesthesia for a nasal biopsy without anesthesiologist medical direction appends modifier QZ to CPT 00164. This communicates to the payer that no physician medical direction relationship existed. If the CRNA is working under an anesthesiologist’s medical direction, modifier QX is used instead, and the supervising anesthesiologist reports modifier QK on a separate claim for the same encounter.
When Is Modifier 23 Required With CPT 00164?
Modifier 23 (Unusual Anesthesia) is required when general anesthesia or MAC is provided for a nasal biopsy that would ordinarily be performed under local anesthesia by the surgeon without a separate anesthesia provider. The anesthesia record must document the specific clinical reason — such as a pediatric patient requiring general anesthesia, a patient with severe anxiety or movement disorder, or significant cardiopulmonary comorbidity making local-only anesthesia unsafe.
How Is Anesthesia Time Calculated for a CPT 00164 Claim?
Anesthesia time starts when the anesthesiologist or CRNA begins preparing the patient for induction — not when the surgeon begins the biopsy — and ends when the patient is safely transferred to post-anesthesia care personnel. Under Medicare, time is divided into 15-minute increments carried to one decimal place (e.g., 34 minutes = 2.3 units). Commercial payers vary; some round to the nearest whole unit. The total units billed equal base units plus time units, multiplied by the applicable conversion factor.
Does Medicare Recognize Physical Status Modifiers for CPT 00164?
Medicare does not add payment for physical status modifiers (P1–P6) appended to CPT 00164 or any other anesthesia code. These modifiers are informational only under Medicare and do not increase the allowable. Most commercial payers, by contrast, do add units for P3 (+1 unit), P4 (+2 units), and P5 (+3 units), making accurate physical status documentation critical for commercial anesthesia billing teams.
Can the Surgeon Bill CPT 00164 for Administering Local Anesthesia During an Intranasal Biopsy?
No. CPT 00164 is exclusively an anesthesia provider code and may only be reported by the anesthesiologist, CRNA, or anesthesiologist assistant who provided separate anesthesia management. Local anesthesia administered by the operating surgeon as part of the surgical procedure is inherently bundled into the surgeon’s procedure code (e.g., 30100) and is not separately billable on either the surgeon’s or anesthesiologist’s claim.
Key Takeaways for Billing and Coding CPT 00164
- CPT 00164 is the anesthesia code for soft tissue biopsy of the nose and accessory sinuses and carries 5 ASA base units — identical to the NOS code 00160, but more specific when a biopsy is documented.
- Payment follows the Standard Anesthesia Formula: (Base Units + Time Units) × Conversion Factor; physical status units add value for most commercial payers but are informational only under Medicare.
- The 2025 Medicare Anesthesia Conversion Factor is $20.3178; the 2026 base units are unchanged from prior years.
- Modifier 23 must be appended — with supporting documentation — whenever general or MAC anesthesia is provided for what payers may consider a local-anesthesia-appropriate procedure.
- Provider role modifiers (AA, QZ, QX, QK, AD, QS) are mandatory on every anesthesia claim; omitting them is a top-five denial reason in anesthesia revenue cycle.
- The surgical biopsy code (e.g., CPT 30100 or 31237) appears on the surgeon’s claim, not the anesthesia claim — crossover billing is a compliance risk.
- When the surgeon performs a more complex nasal or sinus procedure during the same session, the anesthesia code for the most resource-intensive service governs; do not report 00164 if FESS or radical sinus surgery was also performed.
For authoritative payment data, consult the CMS Anesthesiologists Center for current conversion factors and the CMS Medicare Claims Processing Manual, Chapter 12, Section 50 for medical direction documentation requirements. The AMA CPT code set remains the authoritative source for descriptor language, and the ASA Relative Value Guide governs base unit assignments used by Medicare and most commercial payers.
