The Catheter Flushing Method Shows a Similar Diagnostic Yield to the Conventional Method in Brushing Cytology for Biliary Strictures

<bold>Background/Objectives</bold>: Endobiliary brushing is usually performed in the diagnosis of indeterminate biliary strictures; however, in this setting, brush cytology is limited by a low diagnostic yield and sensitivity. Here, we compared the catheter flushing method (CFM) with the conventional cytologic method (CCM) in terms of cellularity and diagnostic performance. <bold>Methods</bold>: Endobiliary brushings were obtained during endoscopic retrograde cholangiopancreatography (ERCP) from patients with biliary strictures enrolled at six tertiary hospitals. Additionally, the CFM was performed after brushing. Using liquid-based cytologic preparations of samples, we assessed the diagnostic performance of the CCM using Pap staining and the CFM using methionyl-transfer RNA synthetase 1 (MARS1) immunofluorescence staining. <bold>Results</bold>: From a total of 399 patients (malignant, 253; benign, 146), 374 CCM samples and 361 CFM samples contained adequate cells, with no significant difference in diagnostic yield (93.7% vs. 90.5%, respectively; p = 0.088). The sensitivity of the CFM (90.3%) was significantly higher than that of the CCM (75.1%; p < 0.001), with no significant difference in accuracy between methods (81.2% vs. 82.6%, respectively; p = 0.608). <bold>Conclusions</bold>: The diagnostic yield of the CFM was comparable to that of the CCM. Additionally, the diagnostic performance of the CFM was comparable to that of the CCM. These findings indicate that the CFM could be an additional brush cytology method for sample collection in patients with indeterminate biliary strictures. Incorporating both the CCM and CFM might be expected to improve the diagnostic yield of brush cytology in the biliary strictures. Further prospective comparative studies between the CCM and CFM using the same staining method are needed to validate these findings.