Handling and measurement
U-100 / U-40 / U-500 Scale
Last updated
The U number on an insulin syringe says how many units the barrel packs into one millilitre, which is what fixes the volume of a single mark. U-100 means 100 units per mL, so one unit is 0.01 mL. U-40 means 40 units per mL, so one unit is 0.025 mL, two and a half times larger. U-500 means 500 units per mL, so one unit is 0.002 mL, one fifth the size.
Why it matters here
The same spoken number means three different volumes on these three barrels. Ten marks counted on a U-40 syringe is two and a half times the liquid that ten marks is on a U-100, so a barrel swapped without noticing changes the volume delivered while the number you counted stays the same.
What it is not
The U number belongs to the syringe you are holding, not to what is in the vial. It was originally a matching system, where U-40 insulin was drawn with a U-40 syringe, and that pairing does not exist for a vial you reconstituted yourself, so the only thing the U number tells you there is how much liquid one mark holds. U-40 barrels are now mostly sold for veterinary use and U-500 for concentrated insulin, which is exactly how a mismatched one ends up in a drawer.
Also called
- u-100
- u100
- u-40
- u40
- u-500
- u500
- u scale
- u-100 scale
- u-40 scale
- u-500 scale
- units per ml
- 100 units per ml
The U simply stands for units per millilitre. People write U100, U-100 and 100 units per mL for the same scale, and the figure is normally on the packet rather than on the barrel of every syringe.
Compounds carrying this term
None on file yet. This term is in the controlled vocabulary but no compound record currently uses it — which is a statement about our coverage, not about the term.