A bilirubin concentration > 10 mg / dL (> 171 micromol / L) in preterm infants or > 18 mg / dL (> 308 micromol / L) in term infants warrants additional testing, including hematocrit, blood smear, reticulocyte count, direct Coombs test, total serum bilirubin and direct serum bilirubin concentrations, and blood type and Rh group of the infant and mother.