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.