Red blood cell distribution width is associated with renal tubular injury in individuals with type 2 diabetes

Aims/Introduction Red blood cell distribution width (RDW) is a parameter of erythrocyte volume heterogeneity that has been traditionally used as an indicator of anemia and other hematopoietic abnormalities. Although the RDW‐coefficient of variation (RDW‐CV) increases in individuals with diabetes, its clinical significance in diabetic kidney disease (DKD), including glomerular and tubular injury, is unclear. Therefore, we aimed to clarify the relationship between RDW‐CV and DKD indices in individuals with type 2 diabetes. Materials and Methods This was a multicenter, retrospective, cross‐sectional study. In 490 Japanese individuals with type 2 diabetes (309 men and 181 women), multiple regression analysis was performed to examine the degree of association between DKD indices (estimated glomerular filtration rate (eGFR), urinary albumin‐to‐creatinine ratio (uACR), log‐transformed uACR (Log‐uACR), urinary liver‐type fatty acid‐binding protein (uL‐FABP)‐to‐creatinine ratio (uL‐FABPCR), and log‐transformed uL‐FABPCR (Log‐uL‐FABPCR)) and clinical confounding factors, including RDW‐CV. Results No significant associations were identified between RDW‐CV and eGFR, uACR, or Log‐uACR in either the simple or multiple linear regression analyses. However, significant and independent positive associations between RDW‐CV and both uL‐FABPCR and Log‐uL‐FABPCR were identified in multiple regression analyses ( P = 0.002 and P = 0.034, respectively). Additionally, logistic regression analysis showed that RDW‐CV was an aggravating factor for the incidence of advanced tubular injury [odds ratio, 1.241 (95% confidence interval: 1.010–1.520), P = 0.037]. Conclusions RDW‐CV was independently and positively correlated with urinary excretion of L‐FABP. Therefore, RDW‐CV may be a simple and useful biomarker for detecting renal tubular injury in individuals with type 2 diabetes.