Background: Non-Hodgkin lymphoma associated hemophagocytic lymphohistiocytosis (NHL-HLH) in adult secondary HLH (sHLH) is a common and universally highly lethal critical disorder. Hyponatraemia is the most common electrolyte disorder in the critical illness setting and acts as a negative prognostic factor. The aim of our study was to evaluate the prognostic role of hyponatraemia among patients with NHL-HLH. Methods: This retrospective study enrolled 153 newly diagnosed adult NHL-HLH patients,

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... ich were divided into 2 groups based on serum sodium concentration on admission, a hyponatraemia and a normonatraemia group. Univariate and multivariate Cox regression analysis were used to identify the prognostic factors associated with worse survival. The overall survival time of all the patients were compared using log rank tests. Restricted cubic splines were conducted to address the association between serum sodium concentration and the risk of mortality. Results: The results showed that 81 (52.9%) patients had hyponatraemia. After a median follow-up of 47 (range 14-180) days, there were 72 (88.9%) cumulative deaths in hyponatraemia group while 50 (69.4%) in normonatremia group. Univariate Cox regression analysis showed that hyponatraemia group demonstrated unfavourable overall survival (P = 0.002). After adjustment for confounders, multivariate analysis revealed that hyponatraemia was an independent prognostic factor for OS (Hazard ratio [HR]:1.51, 95% confidence interval [CI]: 1.03-2.20; P = 0.033). Restricted cubic spline confirmed a linear and positive association between serum sodium and the risk of mortality. Conclusions: Hyponatraemia is relatively frequent in NHL-HLH. As a readily available biomarker in clinical routine, it was a promising prognostic predictor for NHL-HLH.