I'm new to Family Practice. Does anyone have any experience with billing Medicare Secondary (Cahaba in TN) for a lab code that has been sent to a reference lab? An example is 80053,90 billed to Medicare. Medicare returns as unprocessable MA130 and CO4 (procedure code is inconsistent with the modifier or a required modifier is missing). I spoke to a rep at Cahaba Medicare this morning, who told me that this particular modifier is invalid for the provider's specialty and I need a different modifier. Of course, she wouldn't tell me what that modifier was. This is a family practice physician who operates in a rural health clinic. Wasn't sure if that made a difference. Also, the reference lab is noted on the claim. I would greatly appreciate any help on this. Thanks.