Background 80%–90% of patients with SLE report fatigue to be the single most debilitating symptom of their disease. Functional Iron Deficiency (FID), a state of inefficient iron utilisation, has recently been linked with fatigue in a number of conditions. Red Blood Cell Distribution Width (RDW) is a convenient marker of FID.
Purpose To study the relationship between FID (as measured by RDW) and fatigue in patients with SLE.
Methods Three cohorts were recruited and all patients were required to fulfil ACR criteria of lupus.
Juvenile–onset SLE Cohort at University College London Hospital (UCLH), London (UK)
Adult Cohort at UCLH, London (UK)
Adult Cohort at Liverpool Hospital, Sydney (Australia)
In cohorts 1 and 3, patients completed the FACIT Fatigue Score. This generates a numerical score (between 0–52), where a lower score represents more fatigue. In cohort 2, fatigue was measured using the SLE-specific quality of life index, LUPUS QoL. This includes a score of vitality level (a lower score is suggestive of more fatigue). RDW was recorded, in addition to standard markers of lupus disease activity including Erythrocyte Sedimentation Rate (ESR), Complement C3, anti-double-stranded DNA binding (anti-dsDNA), C-reactive protein (CRP) and SLEDAI/BILAG. Spearman’s rank was used to analyse variables with a p-value of <0.05 considered significant.
Results In cohort 1, 72 patients aged 14–42 (median 21) were recruited. FACIT score did not correlate with anti-dsDNA (p=0.4), C3 (p=0.06), ESR (p=0.06), CRP (p=0.1) or SLEDAI (p=0.6). There was a strongly significant correlation between FACIT and RDW (p≤0.001; r=−0.44); figure 1. In cohort 2, 106 patients were recruited aged 18–75 (median 44.5). RDW correlated with ESR (p=0.03; r=−0.20), BILAG (p=0.002; r=−0.30) and vitality scores (p=0.02; r=0.23); figure 2. In cohort 3, 47 patients aged 19–75 (median 46) were recruited. FACIT correlated with RDW (p=0.03; r=−0.32); figure 3.
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