Conversion to use U100 Syringes with U40 Insulin, Diabetic Cat Care

The information contained in this sticky is provided for educational purposes only and is not intended to replace veterinary advice. The intention of this sticky is to open doors to understanding about the specific medical condition or topic, allowing for educated and on-going discussion with your vet.

Never try to do the reverse and use U40 needles with U100 insulin - this is VERY dangerous!

Please note, U40 insulin syringes with half unit markings aren't always easy to find, but they are available. If you can, either ask your vet to order them for you, or save yourself some money by ordering online from ADW through DCC's Affiliate Program - doing so means we can earn small commissions to pay site costs and help fellow members.

It may be recommended that if you are using U40 strength intermediate-action insulin types, particularly if your cat is "sensitive" to small amounts of insulin, that you switch from U40 syringes to U100 3/10cc syringes (for 30u or less) with half unit markings in order to more accurately measure much smaller insulin doses, here's an example of syringes with half unit marks. ) With U100 syringes, a unit of U40 insulin can be broken down into five 0.2u increments (5 x 0.2u = 1.0u). This makes smaller changes to dosing much easier and far more accurate as you are not eyeballing your measurements and hoping like heck to get the amount right consistently.

Below is the conversion chart used to measure draws on the syringe, and below that is an adjusted starting scale in 0.2u increments for using U40 insulin with U100 syringes.

Please be aware that there are several sizes of U100 needles, each holds different amounts of fluid - 3/10cc/ml, 1/2cc/ml and 1cc/ml. The 3/10cc and the 1/2cc both have draw lines on the barrel that equal one unit, while each of the draw lines on the 1cc syringe equals two units. It is important NOT to buy the 1cc syringes, as the 2u draw lines can make it very easy to overdose! If you have 1/2cc syringes, please ask on forum for assistance to create a dosing scale appropriate for the syringe size.

We recommend you buy only 3/10cc syringes for 30 units of insulin with half unit markings!

As far as the conversion goes, what you are dealing with is a "volume" issue when using U100 syringes, compared to U40 syringes. If you hold a U100 syringe beside a U40 syringe, you will notice the U40 syringe is a lot "fatter" than the U100 syringe. If you were to take 1.0u and fill each syringe, you would see that it looks like there is a lot more insulin in the U100 syringe than in the U40 syringe. This is because U100 insulin is pure insulin, while U40 is diluted with water or saline - i.e., U40 is 40% insulin and 60% water, so the water adds more volume to the insulin, making it look like more. A unit of U100 is one unit of insulin, and a unit of U40 is one unit of insulin with 60% more water added to it - both are still one unit of insulin.

It helps sometimes to do an experiment - talk a tall milk glass (the U40 syringe) and pour exactly 1 cup of water into it. Then take a champagne flute (the U100 syringe) and pour exactly 1 cup of water into that. You will see that the milk glass (U 40 syringe) is approximately half full, while the champagne flute (U100 syringe) is almost filled to the top.

When drawing U40 insulin into a U100 syringe, there are two steps to preparing your dose. First, identifying the amount of the dose. Second, identifying the DRAW on the syringe. The conversion factor for volume is 2.5 B meaning that if you need 1.0u of U40 insulin, you need to DRAW to the 2.5 line on the U100 syringe. You will identify the amount of your insulin dose on the conversion chart, then move across the line on the chart to identify the amount of the DRAW on your syringe.

You will need to adjust the way you keep your off-forum test log, adding a column to record the DRAW on the syringe, as well as the dose amount. You want to post only the ACTUAL DOSE on your DCC test log - the DRAW amount is for your records only.

Always, double and triple check that you have got the right DRAW amount for your dose.

Once you make the switch, put the U40 needles far away somewhere (in a completely different place). You don't want to be using a U40 syringe by mistake as you will be giving 2.5 times more insulin than you think!

Please scroll down past the conversion chart for a copy of the dosing scale for U40 insulin types which indicates both amount of insulin and the "draw to" amount, which can be copied and pasted directly to your test log.

0.2	0.5
0.4	1.0
0.6	1.5
0.8	2.0
1.0	2.5
1.2	3.0
1.4	3.5
1.6	4.0
1.8	4.5
2.0	5.0
2.2	5.5
2.4	6.0
2.6	6.5
2.8	7.0
3.0	7.5
3.2	8.0
3.4	8.5
3.6	9.0
3.8	9.5
4.0	10.0
4.2	10.5
4.4	11.0
4.6	11.5
4.8	12.0
5.0	12.5
5.2	13.0
5.4	13.5
5.6	14.0
5.8	14.5
6.0	15.0
6.2	15.5
6.4	16.0
6.6	16.5
6.8	17.0
7.0	17.5
7.2	18.0
7.4	18.5
7.6	19.0
7.8	19.5
8.0	20.0

Starting Scale for Intermediate-action insulin types when using U100 syringes and U40 Insulin (adjusted for 0.2u increments) (For example, Vetsulin/Caninsulin, ProZinc, BCP or Summit PZI

151-170......8.3-9.4......0.2u..........0.5
171-185......9.5-10.2.....0.4u...........1.0
186-200.....10.3-11.1.....0.6u...........1.5
201-220.....11.2-12.2.....0.8u..........2.0
221-250.....12.3-13.8....1.0u...........2.5
251-290.....13.9-16.1.....1.2u...........3.0
291-350.....16.2-19.4....1.4u..........3.5
351-410.....19.5-22.7....1.6u..........4.0
411-450.....22.8-25.0...1.8u..........4.5
451-500.....25.1-27.8....2.0u.........5.0