90 modifier

We have a client who owns two labs in two different states. We are using one lab as the billing address. If I want to bill labs run in the other state would I need to use a 90 modifier and list the other states location and outside lab info? Would I use the location address NPI as the rendering provider NPI instead of the billing lab NPI? I've also been told we have to list both labs CLIA #'s on the claims. Or do we need to be be contracted with Medicare in both states and not use the 90 mod.

Does anyone have tips on billing labs that are owned by the same entity but are in two states?

Any info would've helpful I have gotten so many different answers from Medicare.

Thanks

re: 90 modifier

Are the two labs owned as two separate entities (Tax identification purposes) or are they under one Tax ID? If they are under one Tax ID, then one can't be an outside laboratory for the other.