[Edit] The following applies if you have Medicare or Medicaid patients using your lab services. These CMS rules do not apply if you have no Medicare or Medicaid patients using your lab services. Unless you live in a state where they have adopted the CMS rules re. labs regardless of whether you have Medicare and Medicaid patients or not, such as California and New York.
http://www.cola.org/storage/ff03.pdf for starters if you don't know about it. [/Edit]
This is either a physician office lab (POL) or it is not. If it is a POL, you bill under the NPI of the (single) physician who owns it.
Referals to a POL are not allowed. If you are doing that, don't let Medicare catch you. If the doctor has hired physicians that he pays, they can use the lab. If they are not his employees, they may not use it. There are some exceptions allowed if you have a physicians' group - with "group" meeting Medicare's definition of group.
If it is not a POL, the lab must have its own NPI number and
must do its own billing, under it's own CLIA number and NPI number. CMS has gotton serious about this and there are regulations that cover this. State laws may have something to say about this also. They do in California. If your doctor is confused about this, he needs the advice of a health care lawyer. This is not a question you should be answering for him. It is not a question your doctor should be answering for himself - unless he has already been advised by a health care attorney. But if he had been, you wouldn't be here asking questions.
Hint: if more than one doctor is using the lab, you must provide CMS with the CLIA number of the doctor who owns the POL, and the names of all physicians authorized to use the lab. CMS will pass judgement on whether they will allow this list. If they do, and you submit lab bills, you must include the CLIA number and doctor's name who used the facility. CMS will match the name on the HCFA form against the names they have on file for that CLIA #. No name match, no payment. But you will have also likely triggered an audit to find out what you are doing. Payment for everybody can be suspended until CMS satisfies itself re. what is going on. And then there is the state regulations.