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Abstract
Background Chronic obstructive pulmonary disease (COPD) is a multi-system disorder driven partly by diffuse inflammation, malnutrition and haematological aberrations. Because the red blood cell distribution width (RDW) is a surrogate of these anomalies, we hypothesised that it might be of prognostic importance in COPD patients. Additionally, we tested the supposition that iron deficiency (ID) per se could be a prevalent and ominous co-morbidity in these individuals.
Methods We analysed the relation of red cell indices on admission and over time with mortality in 655 consecutively eligible COPD patients (mean±SD age 77±12 y, FEV1 0.85±0.34 l, FVC 1.44±0.60 l, 54% male). Concomitant heart failure, ischaemic heart disease, and neoplasia were exclusion criteria. The combination of a high RDW and low mean cell haemoglobin (MCH) was utilised to identify ID.
Results On admission, an RDW>15%, Hb<12.5 g/dl, MCH<27, and ID were evident in 33%, 31%, 12% and 10% of patients. Compared to those with an RDW≤15%, patients with levels >15% had lower Hbs, lower FEV1s, and longer median (±IQR) hospital stays (9±11 vs 8±8 days, P<0.001). Over a mean period of 40±29 months, 227 (35%) patients died. On Cox proportional hazards analyses, a higher RDW predicted increased mortality (adjusted χ2 16, P<0.0001) independently of age (χ2 11, P<0.001), FEV1 (χ2 5, P<0.03), Hb and creatinine (latter two not retained in model) and provided graded prognostic information (abstract S167 figure 1A) incremental to that of FEV1 (P<0.05 for change in χ2). Over time, 63%, 72%, 65%, and 46% of patients had a rise in RDW, a fall in Hb, a fall in MCH, and evolving ID (rising RDW and falling MCH), respectively. A rising RDW predicted death (adjusted χ2 32, P<0.0001) independently of baseline RDWs and changes in Hb, with an increase greater than 0.03% per month associated with a twofold escalated risk of mortality (Abstract S167 Figure 1B). Evolving ID was also associated with poorer survival (Abstract S167 Figure 1C).
Conclusions An elevated RDW alone and iron deficiency predict an amplified risk of death in COPD and could be utilised for risk stratification or therapeutically targeted to improve outcomes.