Serum ferritin values in neonates <29 weeks' gestation are highly variable and do not correlate with reticulocyte hemoglobin content.

OBJECTIVES: To compare serum ferritin and RET-He values among extremely low gestational age neonates ELGANs with other markers of iron-deficient erythropoiesis. STUDY DESIGN: This is a secondary analysis of the NICHD Darbepoetin Trial. Study data from placebo recipients who had a serum ferritin, a RET-He, and a mean corpuscular volume (MCV) measurement within a 24-hour period were analyzed for correlation. RESULTS: Mixed linear regression models showed no association between ferritin and RET-He at both early (ß = 0.0016, p = 0.40) and late (ß = -0.0001, p = 0.96) time points. Positive associations were observed between RET-He and MCV at baseline, early, and late time points (p < 0.01, =0.01, <0.001, respectively), while ferritin was not associated with MCV at any time point. CONCLUSIONS: Our study shows that RET-He is better correlated with MCV as a marker of iron-limited erythropoiesis than ferritin. The results suggest that ferritin is limited as a marker of iron sufficiency in premature infants. STUDY IDENTIFICATION: FDA IND Number 100138; ClinicalTrials.gov number NCT03169881; NRN ID number NICHD-NRN-0058 (Darbe).