ANC nadir values of healthy children with the Fy(a-b-) phenotype. Dotted lines indicate the degree of neutropenia: mild- ANC, from 1000 to 1500 cells per μL; moderate- ANC, from 500 to 999 cells per μL; and severe- ANC, <500 per μL. Children younger than 5 years had an ANC as low as 100 cells per μL. Children older than 5 years had an ANC as low as 400 cells per μL but rarely had values <500 cells per μL.