The low number of red blood cells is an important risk factor for all-cause mortality in the general population.

Patients with advanced chronic kidney disease (CKD) show decreased hemoglobin levels. We aimed to verify the changes of red blood cell (RBC) number according to glomerular filtration rate (GFR) levels and its influence on the clinical outcome. With the data from routine health checkups of 114,496 adults, we grouped the subjects according to quartile levels of RBC number in each gender. Mortality data were from the National Statistical Office. RBC number was increased with decreasing GFR and/or the presence of a component of metabolic syndrome (MS) in subjects with GFR ≥ 50 ml/min/1.73 m². The estimated mean RBC number of subjects with GFR 89-50 ml/min/1.73 m² was higher compared to those with GFR ≥ 100 ml/min/1.73 m² by ANCOVA. In men, the death rate was the highest in the 1st quartile group (1Q) of RBC number (1.22%), followed by the 2nd quartile group (2Q, 0.42%), the 3rd quartile group (3Q, 0.39%), and the 4th quartile group (4Q, 0.29%) (p < 0.001). The hazard ratio (HR) of death in 2Q, 3Q and 4Q was 0.446, 0.580, and 0.440, respectively, compared to 1Q (p < 0.001). Among men in 1Q group, subjects with hemoglobin < 14.0 g/dL showed higher mortality rate than those with hemoglobin 14.0-14.9 g/dL or ≥ 15.0 g/dL (2.3% : 0.8% : 1.1%, respectively, p < 0.001). In conclusion, the RBC number was increased according to declines of GFR in the range of GFR ≥ 50 ml/min/1.73 m² and was an important risk factor for mortality.