Reconciling markedly discordant values of serum ferritin versus reticulocyte hemoglobin content

Objective To determine why serum ferritin and reticulocyte hemoglobin (RET-He), drawn to assess neonatal iron sufficiency, sometimes have markedly discordant results. Study design Retrospective records review of five NICUs over 28 months, identifying all patients with a ferritin and RET-He within 48 h. We examined records of all who had marked discordance (one value >95th % reference interval, the other <5th %). Results Of 190 paired ferritin and RET-He measurements, 16 (8%) were markedly discordant. Fifteen of the 16 discordant samples involved a high ferritin and a low RET-He. In these, low MCV and high %Micro-R, and low MCH and high %HYPO-He were present. In total, 8 of the 15 had laboratory or clinical evidence of an inflammatory process and five had suspicion of infection documented. Conclusions When ferritin and RET-He were discordant, erythrocyte microcytosis and hypochromasia suggested that the RET-He gave the more accurate interpretation; that iron deficiency was likely present.