Final answer:
A smaller gauge needle is not suitable for routine blood draws, therapeutic phlebotomy, or drawing a higher volume of blood from donors.
Step-by-step explanation:
The needle gauge that is not suitable for routine blood draws, therapeutic phlebotomy, or drawing a higher volume of blood from donors is a smaller gauge needle (larger number). A larger gauge needle has a narrower diameter, which can cause blood to flow more slowly and cause more pain. For routine blood draws and other procedures, a commonly used needle gauge is 20 or 21, while for higher volume blood draws, a larger gauge needle like 16 or 17 may be used.