AnesthesiaMedium audit riskHCPCS

HCPCS Modifier QX

CRNA Service: With Medical Direction by a Physician

Source: AMA CPT / CMS HCPCS Level II definitions. Maintained by the D3rx Clinical Billing Team.

What modifier QX means

Modifier QX is reported by the Certified Registered Nurse Anesthetist (or anesthesiologist assistant) who furnishes an anesthesia service WHILE medically directed by a physician. It is the non-physician half of a medically directed case and pairs with the directing physician's QK (2-4 concurrent) or QY (one CRNA). The CRNA is paid the medically-directed share, commonly 50% of the fee schedule amount.

When to use it

A CRNA/AA performs the anesthetic under a physician's medical direction that meets the seven steps — reported opposite the physician's QK or QY.

Not sure modifier QX fits your claim? Check it free in Ask D3.Ask D3

Documentation checklist

The record should support every item below before you append modifier QX.

  • That a physician medically directed the case (the paired QK or QY line)
  • The CRNA/AA who performed the anesthesia service
  • The anesthesia record and total anesthesia time/units
  • Support that the directing physician met the seven medical-direction steps

Do NOT use modifier QX when

  • The CRNA worked WITHOUT medical direction — use QZ (full payment)
  • The anesthesiologist personally performed the case — use AA
  • No physician direction occurred but the case was supervised differently — verify the correct provider modifier

Common denial reasons

  • QX billed without a corresponding directing-physician QK/QY claim
  • Documentation doesn't support that medical direction actually occurred
  • Mismatched anesthesia time/units between the CRNA and physician lines

Denial codes you may see with modifier QX

CO-4CO-151CO-59

How to appeal a modifier QX denial

Submit the anesthesia record and the paired directing-physician QK/QY claim showing medical direction, and confirm the anesthesia time/units reconcile across both lines. If the payer questions direction, map the documentation to the seven medical-direction steps the physician met.

Payer notes

QX is the CRNA/AA modifier in a medically directed case and is reimbursed at the medically-directed (typically 50%) rate, with the directing physician billing QK or QY for the other share. The seven medical-direction steps must be met by the physician — without them, the CRNA's service is non-directed (QZ), not QX.

Related & commonly confused modifiers

Modifier QKModifier QYModifier QZModifier QS

Where modifier QX is used

  • Anesthesia services (00100-01999)
  • Care-team anesthesia (physician direction + CRNA/AA)
  • Concurrent medically-directed cases

Got a denial citing modifier QX?

Generate the appeal with Ask D3 — free AI backed by CMS, Medicare, and major-payer data. No signup.

Generate the appeal — freeBrowse all modifiers

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.