MA133 remark code

Remittance advice remark code MA133. Remark codes add detail to the reason code on the same claim line.

Dates fall inside an inpatient stay

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What MA133 means

Some or all dates on the claim fall within an inpatient admission; resend only the services given before or after the stay.

The payer found that some or all of the dates on this claim fall within an inpatient admission. Services during the stay are usually covered under the facility's payment, so the claim cannot be paid as billed.

Drop the dates covered by the stay and resubmit the rest. Check the admission and discharge dates first.

Common causes

• The claim spans dates that include an inpatient admission.
• The patient was admitted from your outpatient or home care service partway through the period.
• The payer's record of the inpatient dates is wrong.

What to do next

1. Confirm the inpatient admission and discharge dates.
2. Rebill only the services given outside the inpatient stay.
3. If the inpatient dates on file are wrong, ask the payer to correct them.

Related codes

• M2 (remark code) Patient was an inpatient at the time
• MA40 (remark code) Missing or invalid admission date
• MA31 (remark code) Missing or invalid billing period dates