A primiparous woman whose blood type is O positive gives birth at term to an infant who has A-positive blood and a hematocrit of 55%. A total serum bilirubin level obtained at 36 hours of age is 12 mg/dL. Which of the following additional laboratory findings would be characteristic of ABO hemolytic disease in this infant?
a) Elevated reticulocyte count
b) Positive Coombs test
c) Low haptoglobin
d) Hyperglycemia