Syringes: A Thorough Breakdown

Let’s talk about a potentially life-saving device, especially if your pup needs insulin or any sort of injection at home… syringes!

We get so many questions regarding syringes, from; “Can I re-use syringes?” to “Can I use these U-40 syringes with U-100 insulin?” to “What is the difference between U-40 and U-100, 1 unit is 1 unit, right”? So, let’s do a thorough breakdown of syringes!

U-40 syringes are used for Vetsulin, Caninsulin, and ProZinc insulins. U-40 insulin has 40 parts of insulin per 1 mL of solution.

U-100 syringes are used for NPH, Glargine, and Detemir insulins. These are human insulins that are used for dogs.  U-100 insulin has 100 parts of insulin per 1 mL of solution.

This means that the barrels of U-40 and U-100 syringes hold different amounts, and this is why it is so crucially important to use the proper syringe for insulin. Using the wrong type of syringe will over-dose or under-dose your dog. There are countries that use U-100 syringes with U-40 insulin, and a conversion is necessary to get the appropriate dose.

Now let’s breakdown an actual syringe!


In order to deliver the insulin into the subcutaneous area, needles must be long enough to get to the appropriate space for proper absorption. AAHA recommends using a ½” (12.7 mm) length needle for most dogs.

We do know that smaller dogs can get away with using the 5/16” (8 mm) length needles without problem. Since a dog’s skin is typically thicker than a human’s skin, it is not recommended to use a 15/64” (6 mm).


Sometimes referred to as “G”, this is the diameter of the needle. The larger the number, the smaller the diameter, so a 31 gauge needle is thinner in diameter than a 29 gauge needle.


The barrel is what holds the insulin. There are unit markings on each syringe for dosing. Depending on the amount of insulin a syringe holds, syringe barrels may have ½ unit markings and 1 unit markings, have 1 unit markings only, and there are syringes that have 2 unit markings.



The plunger is the moveable part of the syringe that draws up and pushes insulin.

This is a lot of information, and syringes can be pretty confusing; especially for those that have never worked in the medical field. Hopefully, this blog helps to clear up any confusion, and if you have any questions or comments, we would love to hear from you! Email, and we’ll be happy to chat! For more great educational conversations, photos, and giveaways, be sure to check out PetTest on Facebook and Instagram.

If you are looking for an online community to join for support, Diabetic Dog Owners and Canine Diabetes Support and Information can be found on Facebook as well.

Be sure to check out for syringes. Just click on the links below to take you directly to the product. Most products on the site offer exclusive iHeartDogs savings with promo code IHEARTSAVINGS at checkout for 30% off! You can take a look through the PetTest flipbook to see their whole line of quality products here:


Advocate U-100 Insulin Syringes 30 G, 0.3 cc, 5/16”

Advocate U-100 Insulin Syringes 30G, 0.5 cc 5/16″

Advocate U-100 Insulin Syringes 30G, 0.3cc, 1/2″

Advocate U-100 Insulin Syringes 31G, 0.3cc, 5/16″

Advocate U-100 Insulin Syringes 31G, 0.5cc, 5/16″


PetTest U-40 Insulin Syringes 31G, 0.3CC, 5/16″

PetTest U-40 Insulin Syringes 31G, 0.5CC, 5/16″

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