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Modified technique of toluidine blue staining in rapid on‐site evaluation

Dear Dr. Bedrossian: Since 2006, our laboratory has been using the modified technique of toluidine blue staining for rapid on-site evaluation (ROSE) of specimens obtained by endoscopic fine-needle aspirations. This technique has been applied so far to almost 200 cases including transbronchial aspirations of pulmonary or mediastinal adenopathies and aspirates of pancreatic tumors obtained by transgastric or transduodenal procedures. After having tested several stainings (including hematoxylin and eosin, Papanicolaou) we selected the toluidine blue technique. This well-known staining is a one-step technique which is inexpensive, simple to perform (requires a limited material and space), and rapid (few seconds only). This technique also results in a very good resolution for the cellular elements (Figures 1A and 2A) and the necrotic background. As it is not a permanent staining, the smears must be restained by Papanicolaou staining, yielding permanent slides (Figures 1B and 2B). We observed the sloughing off of the cellular components once the coverslip was taken off. After many tests by our cytotechnicians, this problem was overcome by preliminary fixation of the smears, before staining with toluidine blue. As fixative, in our laboratory, we use the Delaunay solution because it preserves erythrocytes or cellular structures without any shrinking of the nuclei. Thus the deterioration of morphology mentioned by Joy et al. when they used 95% alcoholic fixative is preserved.