Can anyone tell me how ESRD patient claims can be billed when the principle diagnosis is End Stage Renal Disease. I know that if you add the AY modifier to lab charges that were done at a hospital lab setting on an ESRD patient with the principle diagnosis not being related to the ESRD Medicare will pay. What if your principle diagnosis is ESRD how can you get reimbursement for these lab charges that were done at another facility other than the dialysis center (hospital)?