Red cell distribution width is a predictor of mortality in patients undergoing coronary artery bypass surgery

Abstract

We read with interest the article ‘Red cell distribution width and coronary artery bypass surgery’, by Warwick et al., [1]. They aimed to investigate the effect of red cell distribution width (RDW)—after adjustment for the haemoglobin level—on in-hospital mortality, long-term survival, myocardial damage as assessed by creatine kinase muscle–brain (CKMB) isoenzyme release and the length of hospital and intensive care unit (ICU). They concluded that the RDW was a significant factor determining in-hospital mortality and long-term survival, but that it had no significant effect on CKMB release or length of stay in ICU or hospital. Confounding factor analysis revealed that, in the absence of anaemia, the RDW was still a significant factor determining in-hospital mortality and long-term survival. They suggested that the RDW may be a significant factor determining in-hospital mortality and long-term survival in patients undergoing isolated coronary artery bypass graft (CABG). We believe that these findings will enlighten further studies on the relationships between RDW and coronary artery bypass surgery. Thanks to the authors for their contribution. RDW has recently been identified as an independent predictor of all-cause, long-term mortality in patients with coronary artery disease [2]. Sometimes conditions like the differential diagnosis of anaemias might affect the RDW parameter and so this parameter might be changed in any such abnormality in thyroid function tests, renal or hepatic dysfunction (creatinine >1.5 mg/dl, aspartate aminotransferase and alanine transaminase more than twice the upper limit of normal, respectively), inflammatory diseases and any medication. On the other hand, it is also reported that an increased RDW may be associated with ethnicity and nutritional deficiency (i.e. iron, vitamin B12 and folic acid). Reduced glomerular filtration rate (GFR) may also be associated with adverse outcomes in patients with cardiovascular disease. In a previous study, pre-operative GFR was predictive of all-cause mortality, cardiovascular mortality and combined cardiovascular mortality and morbidity. GFR may be useful in identifying those patients undergoing CABG with subclinical chronic kidney disease [3]. For this reason, it would be better if the authors mentioned any of these possible conditions. Present studies have shown that elevated levels of inflammatory molecules are markers of atherosclerotic disease activity. These molecules also indicate an increased risk of the progression of CABG and they can be reduced by medications such as antihypertensive therapy and acetylsalicylic acid treatment [4, 5]. Additionally, not only RDW but also neutrophil lymphocyte ratio, gamma-glutamyltransferase, C-reactive protein, mean platelet volume and uric acid are markers easily used to assess the cardiovascular disease of the patients [6]. These markers might be useful in clinical practice. RDW itself, alone without other inflammatory markers, may not give information to clinicians about the inflammatory condition and prognostic indication of the patients. So we think that it should be evaluated together with other serum inflammatory markers. Finally, it would be better if the authors defined their timescale for measuring RDW levels, because delay in blood sampling can cause abnormal results in RDW measurements.