Skip to main content

N633 Remark Code: Extra Anesthesia Time Units Denied

N633 means the payer did not allow additional anesthesia time units. It recognized fewer time units than were billed, usually because the documented anesthesia time does not support them or a payer rule limits them.

Quick facts

Code
N633 (RARC N633)
Status
Active In use since July 15, 2013.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The disallowed time units are a provider adjustment and should not be billed to the patient.
Official description
Additional anesthesia time units are not allowed.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N633 means

Anesthesia payment usually combines base units for the procedure with time units for how long anesthesia lasted. N633 says the payer cut some time units: it would not allow the additional units you billed beyond what it recognizes.

It usually appears with CARC 151, 152, or P13 on injury claims.

Common causes

  • Billed units don’t match the documented minutes once the payer applies its conversion rule.
  • Start or end time is missing or unclear in the anesthesia record.
  • Time outside anesthesia care, such as pre-op evaluation or post-op recovery time after handoff, was included.
  • The payer caps time for the procedure or doesn’t allow certain extra units.
  • Minutes were reported instead of units, or vice versa, when the payer expects the other.

How to fix it

  1. Check the anesthesia record for clear start and end times.
  2. Recalculate units using the payer’s conversion rule and reporting format.
  3. Correct the claim with resubmission code 7 if units or format were wrong.
  4. Appeal with the record if your units are supported.

How to prevent it

Make start and end times required fields in the anesthesia record, and set up each payer’s time-reporting rules (minutes or units, and rounding) in your billing system. For unit-related edits generally, see units of service denials.

Codes that may appear with N633

  • CO-151 (Payment adjusted because the payer deems the information submitted does not support this many/frequency of services.): The information submitted doesn't support this many services or units.
  • CO-152 (Payer deems the information submitted does not support this length of service.): The information submitted doesn't support this length of service.
  • CO-P13 (Payment reduced or denied based on workers' compensation jurisdictional regulations or payment policies, use only if no other code is applicable.): Reduced based on workers' compensation jurisdictional rules.
  • N634 (The allowance is calculated based on anesthesia time units.): The allowance is calculated on anesthesia time units.
  • N635 (The Allowance is calculated based on the anesthesia base units plus time.): The allowance is calculated on base units plus time.
  • N203 (Missing/incomplete/invalid anesthesia time/units.): Anesthesia time or units are missing, incomplete, or invalid.

N633 FAQ

How is anesthesia time counted?

Generally from when the anesthesia provider begins preparing the patient for anesthesia to when the patient is safely placed under postoperative supervision. Payers convert minutes to units using their own rules.

What does 'additional' time units mean here?

Units beyond what the payer accepts, whether because documented time is shorter, the payer caps time, or it doesn't allow extra units some billers add.

Can I appeal?

Yes, with the anesthesia record showing documented start and end times that support the units billed.