A mild decrease of renal function is related to increased hemoglobin level during 5-year follow-up period

Background/Aims: We analyzed chronological changes in hemoglobin according to renal function changes over a 5-year follow-up period. Methods: We enrolled 5,266 adults with a glomerular filtration rate (GFR) ${\geq}60mL/min/1.73m^2$ at an initial examination at a routine health check-up; a follow-up examination was conducted 5 years later. We categorized the subjects according to GFR ratio (groups 1, 2, and 3, defined as GFRratio ${\geq}1.00$, 0.75 to 0.99, and < 0.75, respectively). Results: The mean hemoglobin level in subjects with a GFR of 60 to 74 was higher than in those with a GFR of 75 to 89 or ${\geq}90mL/min/1.73m^2$ at the initial examination (all p < 0.001). Among females and males, the frequencies of increased hemoglobin were 46.8% and 40.6% in the GFRratio group 1, 52.4% and 46.1% in group 2, and 59.6% and 52.5% in group 3 over the 5-year period, respectively (all p < 0.001). With multiple logistic regression, group 3 showed 1.594-fold (95% confidence interval [CI], 1.127 to 2.225) and 1.353-fold (95% CI, 1.000 to 1.830) higher likelihoods of increased hemoglobin over the 5-year follow-up period in females and males, respectively. The estimated difference in hemoglobin level was highest in group 3 in both genders. These findings were more evident in subgroups without metabolic syndrome, diabetes mellitus, hypertension, or GFR less than $90mL/min/1.73m^2$. Conclusions: Among a population with GFR ${\geq}60mL/min/1.73m^2$, a mild decrease in GFR over a 5-year follow-up period was associated with an increase in hemoglobin levels.