Correlations between clinical data (age, eGFR) and serum concentrations of GDF-15, TNF-α, and IGF-1. Relationships between laboratory data (age (a), eGFR (b)) and serum concentrations of GDF-15 (Aa,Ab), TNF-α (Ba,Bb) and IGF-1 (Ca,Cb) in males and females. ** p < 0.01, *** p < 0.001.