Which modifier is used when an outside laboratory performs clinical tests on behalf of a physician?

The appropriate modifier used when an outside laboratory conducts clinical tests on behalf of a physician is Modifier 90. This modifier is designated for laboratory services that are performed by an outside laboratory, indicating that the procedure was not performed in the physician's office or in the same facility where the provider is billing. By using Modifier 90, the billing is accurately reflected, acknowledging that the services were provided externally, which can be important for proper reimbursement and documentation in the patient’s medical record.

This context is essential as it helps delineate between services provided directly by the physician and those outsourced to a laboratory. Understanding the specific use of Modifier 90 ensures compliance with billing practices and facilitates clarity in medical recordkeeping.