Red cell distribution width correlates with fatigue levels in a diverse group of patients with systemic lupus erythematosus irrespective of anaemia status.

OBJECTIVES:Fatigue remains a debilitating feature of systemic lupus erythematosus (SLE). Although in some cases this may be the result of intercurrent fibromyalgia, mood disorder or untreated metabolic syndrome, in many cases the cause is unclear. The aim of this study was to investigate the relationship between fatigue and red cell distribution width (RDW), a measure of variability in erythrocyte size and volume. METHODS:A total of 225 patients were recruited from three clinics in England and Australia. Patients completed the Functional Assessment of Chronic Illness Therapy (FACIT) Fatigue Score or 12-item Short Form survey (SF-12) to measure fatigue, which was compared with RDW and haemoglobin. In a subgroup of 72 patients, markers of disease activity were also assessed for correlation with fatigue using univariate and multivariate analysis with fatigue as the dependent variable. RESULTS:In all three groups, significant correlations between fatigue and RDW were observed (p<0.001; p=0.02; p<0.001 respectively) and this was preserved in multivariate analysis. There was no correlation between fatigue and haemoglobin in two groups (with the correlation between RDW and fatigue remaining significant in non-anaemic patients in the third group). In subgroup analysis, fatigue was not associated with any measures of disease activity. CONCLUSIONS:We report a reproducible, statistically significant association between RDW and fatigue levels in a diverse population of patients with SLE. The findings of this study raise the possibility of a potential novel biological basis for fatigue in those in whom there is a lack of an alternate explanation.