U-40 vs U-100 Insulin and Syringes

If you are buying syringes online, or buying insulin on Craigslist be aware of the difference between U-40 and U-100.  U-40 insulin contains 40 ‘units’ of insulin per CC of liquid.  U-100 insulin contains 100 ‘units’ of insulin per CC of liquid.  If your insulin is U-40 then you must use U-40 syringes with it.  Likewise, if your insulin is U-100 then you must use U-100 syringes with it.

The syringe on the left is a U-100 syringe.  It is labelled “U-100” on the barrel.  The barrel is smaller in diameter that the U-40 syringe.  The markings are closer together.

The syringe on the right is a U-40 syringe.  It is labelled “U-40” on the barrel.  The barrel is larger in diameter. The markings are farther apart.

If your insulin is U-100 and you use a U-40 syringe then you will be giving your cat 2.5 times the amount of insulin he/she is supposed to be receiving.  This could be deadly.

Likewise, if your insulin is U-40 and you use a U-100 syringe then you will be giving your cat only 40% of the insulin he/she should be receiving.

Bottom Line: Make sure your syringes match your insulin.