This chart breaks down who is responsible for the charges:
| Modifier | Did the patient sign the ABN? | What does using this modifier mean? |
| GA | Yes | The service is covered by Medicare only under certain circumstances. When you use this modifier, the patient is held financially responsible for the service if it is denied by Medicare. |
| GY | No | The service is never covered by Medicare and the patient is always responsible for the service. You are adding this modifier to get a denial from Medicare so the patient’s secondary insurance will pay. |
| GX | Yes | The service is never covered by Medicare, but you got the patient to sign an ABN anyway. You will get an automatic denial from Medicare and then can submit the service to her payer. The patient is fully responsible for the charges. |
| GZ | No | The service is not medically necessary under Medicare rules. The patient either refused to sign or the office forgot, but the frequency of the service or the diagnosis for which the service was rendered does not meet Medicare criteria. The provider is held responsible and cannot charge the patient for the service, and the secondary insurance will not pay because the service was deemed medically not indicated. |
