Insulin is available in a variety of strengths – commonly referred to as U-100 or U-40. A "U" is a unit. The numbers 40 or 100 refer to how much insulin (the number of units) is in a set volume of fluid – which in this case is one milliliter. For example, U-100 has 100 units per milliliter and U-40 has 40 units per milliliter.

It is possible to use a 1 ml (commonly referred to as a TB syringe) for insulin.

So...U-100 insulin is more concentrated. There is essentially 2 ½ times more insulin in a milliliter as compared to U-40.

To go with the different insulin's, there are different insulin syringes that match the insulin. Some syringes are U-40 and others are U-100. It is important to use the right syringe with the right insulin to achieve the correct dosage of insulin. Your veterinarian should prescribe syringes and insulin that match. The bottle and the syringes each should indicate if they are U-100 or U-40. Again, make sure they match.

It is possible to "convert" and mix and match the insulin syringes.

1 unit of U-40 insulin is 0.025 ml in a regular syringe

1 unit of U-100 insulin is 0.01 ml in a regular syringe

Using non-matching equipment is not ideal and should only be done after consulting with your veterinarian and confirming the "dose" and what equipment you have (it is ideal to have someone double check you and your math – this is no place for experiments or errors!).

Find convert U-40 insulin to a U-100 syringe – please read: How to Convert U-100 and U-40 Insulin and Syringes

IMPORTANT: Make sure that you communicate with your veterinarian prior to any changes. It is important that he or she know exactly how much insulin your cat is getting. Because of the "conversion" – you need to be sure to tell them – the type of insulin and strength (U-100 or U-40), the type of insulin syringe (U-40 or U-100) and the amount so they can really determine how much insulin your cat is getting.

Although matching insulin and syringes is ideal, on occasion, an owner will find themselves with insulin and syringes that don't match. Below is a conversion chart to help in those situations. You will find the amount you need to use with the conversion next to it.