RetiredPremera BluecrossPolicy N/A

Modifier 23 - Unusual Anesthesia

Defines when the Plan recognizes and reimburses services appended with anesthesia Modifier 23 (Unusual Anesthesia) on professional claims across Premera Blue Cross and affiliated lines of business. Applies to anesthesia CPT codes 00100-01999 and sets documentation, modifier sequencing, and exclusions.

Policy Summary

PayerPremera Bluecross

PolicyModifier 23 - Unusual Anesthesia

Policy CodePolicy N/A

Change TypeArchived / Clarifications

Effective Date

Next Review Date

Key ActionProviders must sufficiently document the unusual circumstances in the member's medical records to support use of Modifier 23 when general or monitored anesthesia is required for a procedure that normally does not require it.

SourceLink

POLICY UPDATE CHANGES

Policy archived effective April 2, 2026.

Clarified that Modifier 23 is not appropriate with moderate/conscious sedation codes (99151-99153, 99155-99157).

Clarified that the performing surgeon would NOT append Modifier 23 to the main surgical procedure but continue to append modifier 47 only when they perform anesthesia.

Clarified that Modifier 23 is added after the primary anesthesia modifier which identifies performance/supervision.

1Primary coverage stance

00100-01999Applicable CPT range

99151-99153, 99155-99157Excluded CPT codes (sedation)

The Plan recognizes Modifier 23 (Unusual Anesthesia) for professional claims when appended to an anesthesia procedure that normally does not require anesthesia or local anesthesia but must be performed under general or monitored anesthesia due to unusual circumstances; these circumstances must be documented in the member's medical record. Modifier 23 is used only with CPT codes 00100-01999 and must be sequenced after the primary anesthesia modifier (Modifiers AA, AD, QK, QS, QX, QY, QZ).

This policy is overseen by the Payment Integrity Oversight Committee. The policy underwent regular annual reviews (most recent review date: 2026-03-12) and the document is RETIRED and archived effective April 2, 2026.

Recognition criteria for Modifier 23 (Unusual Anesthesia)

Recognition of Modifier 23 - Unusual Anesthesia

The Plan recognizes Modifier 23 when ALL of the following are met:

Unusual anesthesia requirement: Modifier 23 is appended to an anesthesia procedure that normally does not require anesthesia or local anesthesia and must be performed under general or monitored anesthesia as a result of unusual circumstances.
Documentation requirement: The unusual circumstances are sufficiently documented in the member's medical records.
Documentation must be present in the member's records.
Allowed procedure codes: Modifier 23 is used only with general or monitored anesthesia procedure codes (CPT codes 00100-01999).
Exclusion - sedation codes: Modifier 23 is not appropriate to be appended to moderate/conscious sedation codes (99151-99153, 99155-99157).
Modifier 23 is not appropriate with moderate/conscious sedation codes (99151-99153, 99155-99157).
Modifier sequencing: Modifier 23 is added after the primary anesthesia modifier which identifies whether the service was personally performed, medically directed, or medically supervised (Modifiers AA, AD, QK, QS, QX, QY, QZ).
Sequence: primary anesthesia modifier then Modifier 23.
Surgeon-provided anesthesia reporting: If a surgeon provides the general or monitored anesthesia during the surgical procedure they are performing, the surgeon reports their services by adding modifier 47 (Anesthesia by Surgeon) to the main surgical procedure only and does not bill a separate anesthesia code (00100-01999).
Performing surgeon should not append Modifier 23 to the main surgical procedure; modifier 47 remains appropriate.

Codes and modifiers

Allowed Anesthesia Procedure Codes for Modifier 23CPTCovered

00100-01999

General or monitored anesthesia procedure codes — Modifier 23 allowed when criteria met

Primary Anesthesia Modifiers (must precede Modifier 23)Modifier

AA	Anesthesia services performed personally by the anesthesiologist
AD	Medical supervision by physician: more than four concurrent anesthesia procedures
QK	Medical direction of two, three, or four concurrent anesthesia procedures involving qualified individuals
QS	Monitored anesthesia care
QX	CRNA service: with medical direction by a physician
QY	Medical direction of one CRNA by an anesthesiologist
QZ	CRNA service: without medical direction by a physician

Modifier Not Appropriate / Excluded CodesCPTNot Covered

99151-99153	Moderate/conscious sedation codes — Modifier 23 not appropriate
99155-99157	Moderate/conscious sedation codes — Modifier 23 not appropriate

Anesthesia by SurgeonModifier

47	Anesthesia by surgeon — surgeon should append modifier 47 to main surgical procedure when they provide anesthesia; should not bill separate anesthesia code

Billing, documentation, and audit guidance

Documentation Required

Document unusual circumstances

When Modifier 23 is used, providers must document the unusual circumstances that required general or monitored anesthesia in the member's medical record. Documentation should describe the specific clinical reasons the procedure, which normally does not require anesthesia or local anesthesia, required general or monitored anesthesia and must be retained in the member’s records to support the modifier.

Clinical description of the unusual circumstance requiring anesthesia
Evidence in the member medical record supporting need for general or monitored anesthesia

Billing Rule

Modifier sequencing

Report the primary anesthesia modifier first (one of AA, AD, QK, QS, QX, QY, QZ) to indicate performance/supervision, then append Modifier 23 when criteria are met. Do not append Modifier 23 to moderate/conscious sedation codes (99151-99153, 99155-99157).

Primary anesthesia modifiers (must precede Modifier 23): AA, AD, QK, QS, QX, QY, QZ
Modifier to append after primary modifier: 23
Sedation codes where Modifier 23 is not appropriate: 99151-99153, 99155-99157

Billing Rule

Surgeon-provided anesthesia reporting

If the surgeon provides the general or monitored anesthesia during the surgical procedure they are performing, the surgeon should append modifier 47 (Anesthesia by Surgeon) to the main surgical procedure and should not bill a separate anesthesia code (CPT range 00100-01999).

Modifier: 47 (Anesthesia by Surgeon)
Affected CPT range (do not bill separately if surgeon provides anesthesia): 00100-01999

Denial Risk

Claim denial/audit risk for unsupported Modifier 23

Claims with Modifier 23 that lack sufficient documentation of the unusual circumstances or that are appended inappropriately (for example, appended to moderate/conscious sedation codes) may be subject to denials, increased audits or monitoring, contractual penalties, or contract termination.

Potential consequences: claim denial, audits/monitoring, performance guarantee contractual penalties, or contract termination

Key definitions

Modifier 23 — Definition and key points

TermModifier 23

DefinitionUsed when general or monitored anesthesia is required for a procedure that normally does not require anesthesia or local anesthesia due to unusual circumstances.

DocumentationUnusual circumstances must be sufficiently documented in the member's medical records.

Applicable codesGeneral or monitored anesthesia procedure codes CPT 00100-01999 (Modifier 23 used only with these codes).

Modifier sequencingAppend Modifier 23 after the primary anesthesia modifier (AA, AD, QK, QS, QX, QY, QZ).

Exclusions/NoteModifier 23 is not appropriate with moderate/conscious sedation codes 99151-99153 and 99155-99157; surgeons providing anesthesia should append modifier 47 to the main surgical procedure and not bill a separate anesthesia code.

Policy revisions and archive

05/27/21added

Added clarification that Modifier 23 is not appropriate with moderate/conscious sedation codes (99151-99153, 99155-99157).

05/19/23corrected

Correction clarifying the performing surgeon would NOT append Modifier 23 to the main surgical procedure and should continue to append modifier 47 when they perform anesthesia.

04/02/26archivedLatest