Iron supplementation is not considered as a doping method; however, it can affect the levels of several biomarkers of the hematologic module of the athlete biological passport (ABP), such as the reticulocyte percentage (%RET) and hemoglobin (HGB) level. Thus, iron injection could be a confounding factor in antidoping analyses. Previous studies have suggested that the HGB level and the expression levels of reticulocyte-related-mRNAs, such as 5'-aminolevulinate synthase 2 (ALAS2) and carbonic anhydrase 1 (CA1), could be promising biomarkers for the ABP and detectable in dried blood spots (DBSs). Therefore, in this study, we examined the impact of iron injection on the levels of these potential biomarkers in DBSs. Reticulocyte-related-mRNAs analyses were performed by RT-qPCR. Ferritin level in DBS was measured with enzyme-linked immunosorbent assay (ELISA) method. Notably, there were no significant effects of iron supplementation on the levels of ALAS2 and CA1 mRNAs but by contrast, the %RET and immature reticulocyte fraction (IRF) measured in whole blood increased significantly following iron injection. As expected, iron supplementation increased the ferritin level significantly in both serum and DBS samples. In conclusion, these findings reinforce the specificity of reticulocyte-related mRNAs in DBSs as biomarkers of blood doping to target in antidoping analyses.