Relationship between red blood cell distribution width and kidney function tests in a large cohort of unselected outpatients

Objective. A strong, independent, association has recently been shown between higher red blood cell distribution width (RDW) and the risk of all-cause death and cardiovascular events. However, the mechanism(s) underlying this association remains unclear. Since impaired kidney function is a well-known risk factor for cardiovascular disease, we assessed whether RDW is associated with decreased kidney function. Material and methods. We cross-sectionally assessed results of RDW, haemoglobin, main corpuscular volume (MCV) and serum creatinine levels in a large cohort of unselected adult outpatients consecutively referred by general practitioners for routine medical check-up. Glomerular filtration rate (GFR) was estimated using the abbreviated Modification of Diet in Renal Disease (MDRD) equation. Results. Cumulative results of RDW, creatinine and other variables were retrieved from the database of our Laboratory Information System for 8,585 adult outpatients over a 3-year period. When participants were grouped according to RDW quartiles, there was a strong, graded, decrease in estimated GFR levels (ranging from 87 +/- 18 to 81 +/- 32 mL/min/1.73 m(2); p < 0.0001). Accordingly, the percentage of participants with estimated GFR < 60 mL/min/1.73 m(2) increased steadily across RDW quartiles (from 5% to 19 %; p<0.0001). In logistic regression analysis, lower estimated GFR strongly predicted higher RDW levels (p<0.0001) independently of age, gender, MCV and haemoglobin values. Conclusions. Our findings suggest that there is ail inverse, graded, association between RDW and kidney function tests in a large cohort of unselected adult outpatients.