Diagnostic flowchart for microcytic anemias caused by inherited defects in iron metabolism or heme synthesis. Genes are given in italics and refer to the disorders of this review (Table 2). After clinical and laboratory assessment, clinicians may proceed to perform a diagnostic workup with either bone marrow smears or gene analysis. Iron parameters should be interpreted in the context of the age of the patient and the given treatment: older patients are more likely to have developed iron overload (increased TSAT and ferritin) due to increased and ineffective erythropoiesis and iron supplementation and transfusions. Note that for some diseases, the decision tree is based on only few patients (Table 2). BMRS, bone marrow ring sideroblasts; DM, diabetes mellitus; FPP, free protoporphyrin; neur. dis, neurologic disease; ZnPP, zinc protoporphyrin. *Patients have normocytic anemia and GOF mutation; ⁺only 1 family described; ^±patients have normocytic anemia and the majority have LOF mutations; ^in rare cases, these patients present with elevated ferritin levels.