Claim frequency code

On an institutional claim, the frequency code is the last digit of the four-digit type of bill on the UB-04. CMS describes that digit as the sequence of this bill in the episode of care and ignores the leading zero, so it reads as the third character¹. Its values cover a single bill for a whole stay, interim bills in a series, late charges, and the two that act on an earlier claim: 7 to replace it and 8 to void it^4,5. On the paper CMS-1500 the code appears only on a resubmission. Item 22 takes 7 or 8 with the payer’s original reference number, and the NUCC says the item is not for original claims². In the 837, professional, institutional and dental claims all carry the code in loop 2300, element CLM05-3^3,6.

A 7 or an 8 tells the payer to find the earlier claim and act on it, so the X12 guide requires the payer’s claim control number for that claim, in a REF segment with qualifier F8, whenever the frequency code marks a replacement or void of an adjudicated claim³. Medicare Part A rejects an adjustment or cancel bill that leaves out the control number of the claim it changes⁴.

The mistake is sending a correction as a new original. Without the frequency code and reference number, the payer sees two claims for the same service and can deny the second as a duplicate. The opposite slip is putting a 7 on a claim the payer rejected. A rejected claim was never adjudicated, so there is nothing to replace, and it goes back as an original.