Developmental changes in serum ferritin and erythrocyte protoporphyrin in normal (nonanemic) children.

We studied 4039 children who were 6 months to 12 yr of age to characterize developmental variations of serum ferritin and erythrocyte protoporphyrin. Age-related descriptive statistics were derived. The -2 SD value for serum ferritin was found to increase progressively from 12 to 21 micrograms/1 with increasing age, while the +2 SD value for erythrocyte protoporphyrin was found to decrease progressively from 65 to 42 micrograms/dl whole blood with increasing age. While the mean serum ferritin value was found to continue to rise throughout the first 12 yr of life, erythrocyte protoporphyrin values were highest at 1 to 2 yr of age, then fell to essentially constant levels after 4 to 6 yr of age. These relationships, as well as the linear relationship of increasing hematocrit and serum ferritin with increasing age, suggest that the rise of hematocrit with age, as previously observed, is associated with improving storage and availability of iron for heme synthesis.