GSTM1 and anemia (phenotype): The experimental results indicate a very good correlation between the NIR-absorbance spectrum of spent dialysate fluid and indicators of anemia and iron levels—RBC (0.93), Hb (0.92), Fe (0.94), TIBC (0.96), FER (0.91), Hct (0.94), MCV (0.92), MCH (0.93), MCHC (0.92) in the blood.