HCPCS Modifier QS
Monitored Anesthesia Care (MAC) Service
Source: AMA CPT / CMS HCPCS Level II definitions. Maintained by the D3rx Clinical Billing Team.
What modifier QS means
Modifier QS is an informational modifier indicating the anesthesia was furnished as Monitored Anesthesia Care (MAC) — a planned service in which the anesthesia provider monitors the patient and manages sedation/analgesia, prepared to convert to general anesthesia if needed. Because QS is informational, it is reported ALONGSIDE the appropriate provider/payment modifier (AA, QK, QX, QY, or QZ), which determines reimbursement.
When to use it
The anesthetic was monitored anesthesia care rather than general or regional anesthesia — for example, MAC for an endoscopy or a cataract procedure — reported in addition to the provider modifier.
Documentation checklist
The record should support every item below before you append modifier QS.
- That the service was monitored anesthesia care (not general or regional)
- The anesthesia record showing monitoring and sedation/analgesia management
- The provider/payment modifier reported alongside QS (AA/QK/QX/QY/QZ)
- Medical necessity for MAC where the payer requires it
Do NOT use modifier QS when
- The anesthetic was general or regional anesthesia (QS is specific to MAC)
- As the only modifier — QS is informational and must accompany the provider/payment modifier
- The encounter was moderate (conscious) sedation by the proceduralist, not anesthesia-provider MAC
Common denial reasons
- QS billed without the required provider/payment modifier
- MAC billed where the payer's policy requires a specific covered indication that isn't documented
- Confusion with moderate (conscious) sedation, which is reported differently
How to appeal a modifier QS denial
Confirm QS was reported alongside the correct provider/payment modifier, and submit the anesthesia record documenting monitored anesthesia care. Where the payer limits MAC coverage, attach the documented indication/medical necessity showing MAC (not moderate sedation) was appropriate.
Payer notes
QS flags MAC for informational purposes and does not itself set payment — pair it with the provider modifier (AA, QK, QX, QY, or QZ). MAC is held to the same standards as general anesthesia, and some payers limit MAC coverage by procedure or require a documented indication.
Related & commonly confused modifiers
Where modifier QS is used
- Anesthesia services (00100-01999) furnished as MAC
- Endoscopy and cataract procedures with MAC
- Procedures where MAC coverage is indication-dependent
Got a denial citing modifier QS?
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Medical billing disclaimer
Modifier definitions follow standard AMA CPT and CMS HCPCS Level II guidance and are for educational reference. Payer policies, billing formats, and coverage rules vary and change. Always verify the current rule with the specific payer before submitting. D3rx is not responsible for claim outcomes.