From where is PKU testing typically collected?

PKU testing, or phenylketonuria testing, is primarily performed on newborns to detect a metabolic disorder that can lead to severe intellectual disabilities if untreated. The preferred method for collecting the sample is through a heel prick, which involves taking a few drops of blood from the heel of a newborn. This is a practical and minimally invasive technique that is particularly suitable for infants, as their veins are not yet well developed for venipuncture. While urine can also be involved in testing for some metabolic conditions, the standard for PKU specifically focuses on blood samples obtained from a newborn's heel.

The other options do not align with the typical practice for PKU testing. Collecting from an adult’s arm or a child’s finger is not standard for this specific test, and drawing from a vein in the leg is generally not done for PKU screening in newborns. Therefore, the heel prick is recognized as the most effective and appropriate method for collecting specimens for PKU testing.