Stress test codes are different than many other diagnostic tests which have two components: a professional component and a technical  component.  Stress tests have three components:

• Technical
• Interpretation and report (physician service)
• Supervision (physician service)

The service may also be billed globally, if the group that owns the equipment also provides the interpretation and report and the supervision.

Here is how the codes look: 93015 is for the global service, and includes all of those services above.  It would be used when the same entity provides all parts of the service.

93016 is the code to use for the physician supervision of the test, without the interpretation and report.

93017 if the techinical component, used for the tracing only, typically by the hospital or facility that owns the machine, hires the staff, rents the office, etc.

93018 is the physician's interpretation and report.

In most instances, when the stress test is owned and operated by the hospital, the hospital bills 93017 and the physician bills 93016 and 93018.  Do not attach any modifiers to these three codes: because the CPT® definition of the codes already breaks down the technical and two professional components, an additional modifier is not needed.