Baseline Red Blood Cell Distribution Width Correlates with Disease Activity and Therapeutic Outcomes in Patients with Systemic Lupus Erythematosus, Irrespective of Anemia Status

Background: Red blood cell distribution width (RDW) has been recently found to reflect systemic inflammation in addition to anisocytosis, and its value for assessing disease activity of systemic lupus erythematosus (SLE) has been addressed in two studies, but its correlation with therapeutic outcomes and disease flare has not been evaluated. Methods: One hundred and ninety-six newly diagnosed patients with SLE (all-SLE), including 105 non-anemic patients (na-SLE) and 91 patients with anemia (a-SLE) were prospectively studied. Baseline RDW of SLE patients was compared with that of control subjects. Correlations between RDW and disease activity, traditional laboratory parameters, clinical features, therapeutic outcomes, and disease flare were examined. Results: RDW was exclusively higher in all-SLE, na-SLE, a-SLE than in controls (p < 0.001), but no significant difference of RDW was found between na-SLE and a-SLE (p = 0.27). More active disease scored with SLE Disease Activity Index 2000 (SLEDAI-2K) was present in patients with elevated RDW (> 15%) than normal RDW (= 11 - 15%) irrespective of anemia status (p < 0.001), and positive correlation between RDW with SLEDAI-2K was also disclosed independent of anemia status (r = 0.576, 0.614, 0.542, respectively for all-, na- and a-SLE, all with p < 0.001). Additionally, RDW positively correlated with high-sensitivity C-reactive protein (hsCRP) in all-SLE (r = 0.352, p < 0.001), na-SLE (r = 0.430, p < 0.001), and a-SLE (r = 0.315, p = 0.002). Among all clinical features, only the incidence of pulmonary arterial hypertension (PAH) was likely to be higher in elevated-RDW SLE than in normal-RDW SLE (chi(2) = 4.135, p < 0.05). Patients received stratified therapy of remission induction based on their disease activity. A significantly higher rate of response (complete and partial response) was observed in normal-RDW than in elevated-RDW patients (all-SLE: 92.2% vs. 74.1%, p = 0.001; na-SLE: 92.3% vs. 77.5%, p = 0.04; a-SLE: 92% vs. 70.7%, p = 0.012). During a 12-month follow-up of the 166 responders, significantly greater flare-free survival was observed in normal-RDW than in elevated-RDW patients (68.8% vs. 29.8%, p = 0.002; 53.6% vs. 28.1%, p = 0.027; 55.9% vs. 31.4%, p = 0.032, respectively, for all-, na- and a-SLE). Conclusions: Our findings suggest that baseline RDW is an easily available parameter not only capable of reflecting SLE overall activity, but also predicting therapeutic outcomes and the risk of disease flare irrespective of anemia status.