Introduction: Monoclonal B-cell lymphocytosis is a symptom free condition characterized by the circulation of small clonal population of B lymphocytes in peripheral blood (less than 5x109/L) expressing an immunophenotype similar to chronic lymphocytic leukemia. Different studies based on big hospital series have manifested a higher risk in subjects with monoclonal B-cell lymphocytosis to progress to a chronic lymphocytic leukemia. The behavior of this hematologic entity is unknown therefore its frequency in sporadic chronic lymphocytic leukemia patient relatives was determined. Methods: Transversal descriptive study, 8 color flow cytometry was performed using two of the tubes of the Euro Flow recommended panel, with modifications, for the diagnose of chronic lymphoproliferative disorders of B lymphocytes; besides, a fluorescence in situ hybridization was performed. univariate and bivariate analyses of the information were performed. Results: Monoclonal B-cell lymphocytosis frequency found in 51 analyzed relatives was 2%, it was a female participant, 59 years old, with a total leukocyte count of 7.7x109/L and a B lymphocyte count of 0.124x109/L; from these, 0.04x109/L were clonal cells with restrictions of the kappa light chain. Rearrangements of the IGH gene (14q32) were found. Conclusion: Monoclonal B-cell lymphocytosis was detected in one relative of a patient with sporadic chronic lymphocytic leukemia in a frequency similar to the one reported in general population.

Introducción y objetivos. La linfocitosis monoclonal de células B(LMB) es una condición asintomática que se caracteriza por la circulación de pequeñas poblaciones clonales de linfocitos B en la sangre periférica (menos de 5 x 109/l), en ausencia de signos clínicos o síntomas de un trastorno linfoproliferativo crónico. El recuento absoluto de células B es el umbral que permite diferenciar la LMB de la leucemia linfoide crónica (LLC). En Colombia se desconoce el comporta miento de esta entidad hematológica, por tal razón se determinó la prevalencia de LMB en familiares de pacientes con LLC esporádica.