Final answer:
For collecting a micro sample from a patient of 18 months, the preferred site is the medial and lateral portion of the foot. This choice avoids more sensitive areas with less developed veins or more nerve endings.
Step-by-step explanation:
When collecting a micro sample from a patient who is 18 months old, the recommended site for collection is a. the medial and lateral portion of the foot. This is because, in young children, the veins in the hands are not as well developed, and the antecubital fossa, which is a common site for venipuncture in older children and adults, may not be suitable due to the small size of the vessels. Additionally, the hand contains more nerve endings which could make the process more painful for the child. The medial and lateral aspects of the heel (plantar surface of the foot) are often used for microsampling in infants and toddlers.