Triage: Bill the patient immediately
The payer sent the money to the patient instead of the practice, most often on out of network claims. Nothing further is coming from the payer on this line; the patient is holding your reimbursement.
This code hides in remittances looking like a denial, gets written off by busy billers, and quietly becomes the most expensive misread in the book. The claim was not denied. It was paid, to the wrong party.
An out of network claim for $240 processes, and the payer sends the check to the patient. The ERA line shows code 100 with nothing payable to the practice. A busy biller reads it as a denial and writes it off. The patient has the practice’s $240 and does not know it, and every week that passes makes the recovery call harder.
Cervica reads the 100 code off the ERA and routes it to patient billing instead of the write off pile, with the reference language ready.
General information for billing teams, not legal or payer specific advice. CARC definitions belong to X12; payer policies vary and control. Verify against the payer contract before acting on any individual claim.