<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>The diagnosis of T‐cell non‐Hodgkin lymphomas (NHL) is challenging. The development of a monoclonal antibody specific for T‐cell receptor β constant region 1 (TRBC1) provides an alternative to discriminate clonal T cells. The aim of this study was to evaluate the diagnostic potential of an anti‐TRBC1 mAb for the identification of T‐NHL.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We performed a cross‐sectional diagnostic analytic study of samples tested for lymphoma. All samples sent for lymphoma screening were first evaluated using the standard Euroflow LST, to which a second additional custom‐designed T‐cell clonality assessment tube was added CD45/TRBC1/CD2/CD7/CD4/TCRγδ/CD3. Flow cytometry reports were compared with morphological and molecular tests.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Fifty‐nine patient samples were evaluated. Within the T‐cell population, cut‐off percentages in the CD4+ cells were from 29.4 to 54.6% and from 23.9 to 52.1% in CD8+ cells. Cut‐off ratios in CD4+ T cells were from 0.33 to 1.1, and in CD8+ cells between 0.22 and 1.0. Using predefined normal cut‐off values, 18 of 59 (30.5%) samples showed a restricted expression of TRBC1. A final diagnosis of a T‐NHL was confirmed clinically and/or by histopathological studies in 15 of the 18 cases (83.3%). There were no cases of T‐NHL by morphology/IHC with normal TRBC1 expression. Non‐neoplastic patient samples behaved between predefined TRBC1 cut‐off values.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>Expression of TRBC1 provides a robust method for T‐cell clonality assessment, with very high sensitivity and good correlation with complementary methods. TRBC1 can be integrated into routine lymphoma screening strategies via flow cytometry.</jats:p></jats:sec>
