L1 Modifier: Reference Labs plus other services?

Our hospital serves as a reference lab for one of the local clinics so we regularly bill on TOB 14X with no modifier for reference labs only.

If that same patient then comes to the hospital for an X-ray (or other service), and it's either ordered by the same physician or not unrelated to the labs, do I need to bill the labs on the 13X with no modifier? Or can I leave the labs on the 14X since it was a non-patient specimen?

We've been doing the first option, but I'm hoping someone has a reference that addresses this situation. The CMS IOM is not helpful here and I can't find any FAQs about it.

Thanks,

Julia

L1 Modifier: Reference Labs plus other services?