I know that there is modifier -90 to use to indicate a lab test was not performed on-site, but rather by an off-site reference lab. My question is: Is there a restriction as to whether or not a facility can or cannot bill for these tests? Is it based on size or staffing of the facility? Or can any facility that sends lab tests out to be performed bill the patient or the insurer for the cost of the tests. Of course, that is to assume that the reference lab itself is not filing claims as well.