Wiki add on codes

there aren't any general guidelines that say that, most times it depends on two things: 1, the code you're using, and 2, the payor. The code matters because some add on codes are specific in their language and that's what doesnt allow for multiple units (example, the "new" facet injection codes, the second level add-on code can only be billed once because it says "second level", same with the third, it says "third and any additional", which eliminates the possibility for additional units). the payor matters because of individual payor guidelines, some will allow you to use one line with multiple units, some require multiple line items, one unit each. you have to know who you're billing. it would be nice if they would all get on the same page and make it easy, but they almost all use different software, and different software calculates things differently, so they have create their own special little rules. does this make sense now? hope I could help! :)