Knowledge Base Article

Q:

What are the Medicare rules for reporting modifier GG?

A:

Modifier GG is defined as the performance and payment of a screening mammogram and diagnostic mammogram on the same patient, same day.

In MMP’s experience, extra mammogram views to further investigate a potential problem seen on a screening mammogram are typically performed on a subsequent day. This allows the radiologist ample time to review the patient’s previous mammograms for comparison. But, additional diagnostic views are sometimes performed on the same day as the screening mammogram, and this creates the scenario for reporting modifier GG.

One of the best CMS references for using modifier GG is in the Correct Coding Initiative (CCI) Policy Manual for Medicare Services, chapter IX, page IX-8, paraphrased here:

Screening and diagnostic mammography are normally not performed on the same date of service. However, when the two procedures are performed on the same date of service, Medicare requires that the diagnostic mammography CPT code be reported with modifier GG and the screening mammography CPT code be reported with modifier 59.

The Medicare Claims Processing Manual, chapter 18, section 20.6 provides some additional information.

• A radiologist who interprets a screening mammography is allowed to order and interpret additional films based on the results of the screening mammogram while a beneficiary is still at the facility for the screening exam. 
• When a radiologist’s interpretation results in additional films, Medicare will pay for both the screening and diagnostic mammogram.
• Providers submitting a claim for a screening mammography and a diagnostic mammography for the same patient on the same day, attach modifier “GG” to the diagnostic mammography. 
• A modifier “-GG” is appended to the claim for the diagnostic mammogram for tracking and data collection purposes.