RARC M55: Missing or Invalid Claim Type or Bill Type
The type of bill code on the institutional claim is missing, invalid, or does not match the services billed — correct the bill type and resubmit.
What Does RARC M55 Mean?
M55 signals that the payer found a problem with the type of bill (TOB) code on an institutional claim. The type of bill is a three-digit code on the UB-04 (form locator 4) that communicates three critical pieces of information: the facility type (first digit), the bill classification (second digit), and the frequency or claim sequence (third digit). For example, TOB 131 means hospital outpatient, admit through discharge, original claim. This code drives how the payer routes and processes the entire claim, so an error here affects everything downstream.
M55 can appear when the TOB field is blank, contains an unrecognized combination of digits, or does not match what the payer expects based on the facility type and services billed. A common scenario is submitting a professional-type service on an institutional claim with the wrong bill classification — for example, using an inpatient TOB when the services were actually provided in an outpatient setting. Another trigger is using an incorrect frequency code, such as submitting a replacement claim (frequency 7) when the payer has no original claim on file to replace.
M55 pairs with CARC 16 (missing information), CARC 252 (additional information required), or CARC 183 (incorrect type of bill). The frequency digit is a particularly common source of errors and can be tricky — using a void (frequency 8) when you meant to submit an adjustment (frequency 7) has very different consequences.
What to Do
Verify the type of bill code against the NUBC guidelines for the facility type and claim circumstances. Confirm that the first digit matches your facility type, the second digit matches the bill classification (inpatient vs. outpatient, for example), and the third digit reflects the correct claim frequency (original, replacement, void, etc.). If the TOB was blank, populate it with the correct three-digit code. If a code was entered but rejected, check whether the combination is valid and accepted by the payer. Correct and resubmit.
For facility billing departments, the most common M55 errors involve the frequency digit. Build a quick-reference guide for your team that maps claim scenarios to frequency codes: original claims (1), cancel/void of a prior claim (8), replacement of a prior claim (7), and final claim in a series (4). If your facility operates multiple service types — inpatient, outpatient, swing bed, home health — ensure that staff selecting the TOB understand which classification applies to each service line.
Common Scenarios
- A hospital submits an outpatient claim with TOB 111 (inpatient, admit through discharge) instead of TOB 131 (outpatient, admit through discharge), causing the payer to reject it for an incorrect bill type.
- A corrected claim is submitted with frequency code 1 (original) instead of frequency code 7 (replacement), and the payer sees it as a duplicate of the original claim rather than a correction.
- A critical access hospital bills a swing bed claim using a standard inpatient TOB instead of the swing bed bill type (TOB 18x), and the payer cannot apply the correct reimbursement methodology.
Commonly Paired With
No common pairings documented yet.