Wiki Anti-Markup Rule

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I understand Medicare requires participating providers to indicate on the claim form in Box 20 that the service was purchased from an outside lab and what that amount is. My question is regarding our charge amount that we report in Box 24-F, can this fee exceed that which is reported in Box 20 or does it have to equal or be of lesser value? I've read some correspondence where CMS clarifies the Anti-Markup Rule for diagnostic tests but I still don't see any reference to a limit on what we can charge. Article states that Medicare pays the lower of: supplier's charge to physicians, billing physician's actual charge or the Medicare fee schedule. And if it does have to be equal (or lesser) then how does this come in to play when you are billing a commercial carrier as we can't have two separate fee schedules. I hope I have provided enough information but if not please let me know.