GSTM1 and anemia: In humans plasma ferritin concentrations between 30 and 45 ng/mL have been proposed for clinical IDA diagnosis (Ioannou et al 2007; Garcia-Casal et al 2021), but like Hb concentration to define anemia there is some debate, with some research suggesting 15 ng/mL is an appropriate threshold (Killip et al 2007).