• Chloé Baillou, Florence Jacomet, Thomas Dejoie, Pierre Lureau, Clément Beuvon, Aurélie Grados, Pauline Martins, Pascal Roblot, Mathieu Puyade, and Mickael Martin.
• Service de médecine interne, maladies infectieuses et tropicales, CHU Poitiers, Poitiers, France.
• Postgrad Med J. 2022 Feb 7.

BackgroundPolyclonal hypergammaglobulinaemia (PH) represents a classic diagnosis problem in internal medicine. However, there is no consensus threshold for PH. The aim of this study was to define a threshold for PH.MethodsWe conducted a retrospective multicentric study using laboratory biological databases between 1 January 2016 and 31 December 2016 in two university hospitals and one non-university hospital. All patients 18 years old or over and with at least one serum protein electrophoresis (SPE) available in 2016 were included. Exclusion criteria were monoclonal, biclonal, or oligoclonal spikes or, in case of hypogammaglobulinaemia, proven free light chain gammopathy. The main endpoint was to define the threshold values for PH in this population. Another objective was to define the 95th percentile of the distribution.Results20 766 SPEs were included in this cohort. The PH threshold on 95th percentile was 18.9 g/L. The threshold varied according to geographical areas.ConclusionsThis is the first study to scientifically define a PH threshold. The main limitation is that our threshold is only biological. The study was not designed to associate this threshold with a clinically active disease. In conclusion, while the 19 g/L cut-off seems the most relevant threshold, but it will need to be validated by prospective studies.© The Author(s) 2022. Published by Oxford University Press on behalf of Postgraduate Medical Journal. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

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