To determine the prevalence of iron deficiency (ID) and iron deficiency anemia (IDA) in a sample of children with Down syndrome (DS) and to evaluate the effect of macrocytosis on the diagnosis of ID/IDA in these children.

Children with DS ≥12 months of age who were followed at the Duke University Medical Center Comprehensive DS Clinic from December 2004 to March 2007 were screened for ID/IDA with a complete blood count, reticulocyte count, iron panel, and erythrocytic protoporphyrins.

A total of 114 children were enrolled, with a median age of 4.7 years. ID was identified in 12 subjects (10%), and IDA was identified in 3 subjects (3%). ID/IDA would not have been accurately diagnosed in 13 of 15 subjects (86%) if red blood cell (RBC) indices alone had been used for screening. Abnormal RBC indices with low transferrin saturation were 100% sensitive for ID/ IDA screening.

Prevalence of ID/IDA in children with DS was comparable with that in the general pediatric population. Macrocytosis had implications for screening of ID/IDA with only RBC indices. We suggest ID/IDA screening in DS children be done with a laboratory panel at least including complete blood count, reticulocyte count, transferrin saturation, and serum ferritin.