ASCP Phlebotomy Technician Certification Practice Exam 2025 - Free Phlebotomy Practice Questions and Study Guide

The primary composition of skin puncture blood comes from capillary blood, but it also includes contributions from arterioles and venules. When a skin puncture is performed, blood is drawn from the very small capillaries located close to the surface of the skin, which are part of the microcirculation. However, because these capillaries are connected to arterioles (small arteries) and venules (small veins), the blood collected during a skin puncture will also contain a mixture from these vessels.

This mixture results in a sample that reflects the overall constituents of the blood, including oxygen and nutrients from the arterioles and some waste products from the venules. Therefore, the choice that identifies the blood from both arterioles and venules appropriately explains the composition of the blood obtained from a skin puncture, making it the correct answer.

In contrast, focusing solely on venous blood or blood exclusively from large arteries does not accurately represent the nature of skin puncture samples. Capillary blood alone is too narrow a definition, as the sample does also derive from arterioles and venules, making the correct understanding about the mixture essential for phlebotomy practice.