Background: Muscle invasive(MIBC) and metastatic (mBCa) bladder cancer patients have few options to extend survival. Recent studies have shown that PD-1 and programmed death-ligand 1 (PD-L1) checkpoint inhibitors have activity even in chemotherapy refractory patients and it has been proposed that PD-L1 expression on tumors or lymphocytes may correlate with response to therapy. To identify potential patients who may benefit from PD-1/PD-L1 targeted immunotherapeutics, we utilized a non-invasive, real-time blood test for PD-L1 protein expression in circulating tumor cells (CTCs) and white blood cells (WBCs) of bladder cancer patients. Methods: Twelve blood samples from unique patients with MIBC or mBCa were collected and shipped to Epic Sciences. All nucleated cells were plated onto glass slides and subjected to IF staining and CTC identification by fluorescent scanners and algorithmic analysis. CTCs, defined as traditional (CK+ CD45- w/ intact DAPI nuclei and morphologically distinct) or CK- (CK-, CD45-, intact and distinct) were identified. PD-L1 biomarker characterization was assessed by IF staining, and UroVysion FISH testing was used to assess genomic abnormalities in a subset of patient samples. Additionally, WBCs (CD45+ cells) were assessed for PD-L1 expression. Results: Traditional CTCs were detected in 6/12 (50%) patients. 3/12 (25%) patients had PD-L1+ cells, 2 of these patients were exclusively CK-/PD-L1+ CTCs, which were confirmed as cancer via FISH. CK- CTCs were detected in 83% (10/12) patients. 5 patients had greater than 4 fold PD-L1 positivity in WBCs as compared to healthy donor controls. Conclusions: MIBC and mBCa patients have detectable CTCs with a high frequency of CK-/PD-L1+ CTCs. Utilization of a liquid biopsy to identify patients with PD-L1+ CTCs and PD-L1+ WBCs may enable both patient selection or short term therapeutic monitoring for measuring pharmacodynamics to ensure therapy effectiveness. Further studies are planned to investigate association of PD-L1+ CTCs and WBCs with response to PD-1 and PD-L1 checkpoint immunotherapy.