HCPCS Modifier GS
Dosage of erythropoietin stimulating agent has been reduced and maintained in response to hematocrit or hemoglobin level.
Guidelines and Instructions
This modifier is used for national claims monitoring for ESAs administered in Medicare renal dialysis facilities, so therefore, is not applicable to Part B.
Reference: CMS Medicare Claims Processing Manual (Pub. 100-04), Chapter 8, Section 60.4 (PDF, 663 KB).