Final answer:
The PKU test on an infant is usually conducted by obtaining a blood sample from the infant's heel. This is commonly done via a heel, which is a safe and straightforward method for newborn screening.
Step-by-step explanation:
A PKU (phenylketonuria) test is typically drawn from the heel of an infant. This procedure, known as a heel or heel stick, involves taking a small blood sample from the baby's heel, which is used for the newborn screening test to check for PKU and other conditions. From an infant, a PKU test would typically be drawn from the heel area. The heel is chosen because it's easier and safer to obtain a blood sample from this spot on a small infant without causing harm to other areas of the body.