Focused instruction

Microcytosis can accompany iron-restricted erythropoiesis, thalassemia-pattern erythropoiesis, inflammation, chronic blood loss, or lead exposure. A relatively preserved red-cell count and target cells can fit a thalassemia pattern. Increased RDW, low ferritin, and low locally interpreted Ret-He can fit iron-restricted erythropoiesis. These patterns can overlap; CBC and smear findings do not establish genotype or exclude a coexisting hemoglobinopathy.

Ferritin reflects iron stores and is also an acute-phase reactant. A low ferritin supports depleted stores, while a normal ferritin with raised inflammatory markers cannot exclude iron deficiency. WHO guidance uses ferritin below 12 micrograms/L for apparently healthy children under 5 years, below 15 micrograms/L for apparently healthy people 5 years or older, and a 30 micrograms/L threshold for children under 5 years with inflammation. Do not apply the under-five inflammatory threshold to all children.

Ret-He, also reported as CHr by some systems, measures hemoglobin in newly produced red cells and reflects recent iron available for erythropoiesis. A low result can support restricted hemoglobinization when the local method, reporting name, pediatric interval, and decision support are declared. It does not independently identify the cause of restricted hemoglobinization, and a Ret-He or CHr cutoff must not be transferred between analyzer families.

Keep morphology, iron evidence, and confirmed hemoglobinopathy results in separate report categories.