By Nadia Shaikh, PharmD, and Jennifer Goldman-Levine, PharmD, CDE, BC-ADM, FCCP
Insulin and other injectable drugs are important tools for the management of both Type 1 and Type 2 diabetes. Insulin is, of course, required for the treatment of Type 1 diabetes, and it is often needed to treat Type 2 diabetes when oral drugs and lifestyle measures no longer adequately control blood glucose levels. Even if you don’t currently take insulin, there’s a decent chance that you will in the future.
Many people are understandably uneasy about the idea of giving themselves injections. Learning more about how insulin injections work, however, usually helps alleviate some fears and concerns. Even if you already take insulin and aren’t experiencing any problems, you may be able to make the process more comfortable or convenient — and head off future problems — by learning more about the process. This article provides an overview of the tools and techniques for giving insulin injections.
Currently, the only way insulin can be delivered to the body is by injection, using either a syringe or an insulin pen, by infusion, using an insulin pump, or via inhalation (not discussed in this article). While there are companies working to develop forms of insulin that can be taken as a pill, none of these products are currently available to consumers.
For decades, a syringe was the only option for injection, until 1985 when the NovoPen was introduced by the company that is now Novo Nordisk. Insulin pens allow users to “dial in” an insulin dose for injection, a process that is generally much faster than measuring a dose with a vial and syringe. The majority of pens are prefilled with insulins and are disposable, with a few available that have replaceable cartridges. Unlike insulin syringes, which come with a fixed needle, insulin pen needles can and should be removed and replaced after each use.
Needle size involves two different factors: length and gauge. The gauge of a needle is how thick the needle is. The higher the gauge, the thinner the needle. Needle gauges range from 29 (the thickest) to 32 (the thinnest). Using a thinner needle both helps the insulin get to the right place (just under the skin) and reduces pain.
The length of a needle is important because if the needle is too short, the insulin will be delivered into the skin (also known as the dermis layer). If the needle is too long, the insulin will be delivered into the muscle. The correct location for insulin delivery is the fat layer, also known as the subcutaneous layer, located between the skin and the muscle.
There is a persistent myth that people who are overweight or obese need a longer needle for insulin injections, and that the elderly and very young have thinner skin that requires a shorter needle. This is simply not true. Research has shown that human skin is about the same thickness regardless of race, sex, age, or weight, ranging from 1.25 to 3.25 millimeters.
It doesn’t matter where in the subcutaneous layer insulin is injected, as long as it reaches this layer. This means that for most people, a needle longer than 3.25 mm is all that is needed to properly administer insulin. Moreover, there is a greater chance of accidentally entering the muscle layer when using a longer needle — especially when using needles longer than 5 millimeters — so longer is not better.
Until relatively recently, the only needle length available for either pens or syringes was 12.7 millimeters (1/2 inch). In 1993, the 8-millimeter pen needle was introduced, which was followed by the 5-millimeter needle in 1999 and the 4-millimeter needle in 2010. For syringes, the 12.7-millimeter needle was joined by the 8-millimeter needle in 1997 and the 6-millimeter needle in 2012. A syringe needle can’t be made any shorter than 6 millimeters because it needs to be long enough to get through the rubber stopper at the top of an insulin vial.
Despite the introduction of shorter needles for syringes and insulin pens, research has shown that 63% of insulin users are still injecting with the same length needle that they were originally prescribed. The most popular needle length is 8 millimeters. However, there is no medical rationale for a needle longer than 6 millimeters, and, in fact, it has been found that blood glucose control is just as good with 4-, 5-, and 6-millimeter needles as with longer ones.
Regardless of needle length, good injection technique is very important for insulin to work properly.
Several areas of the body are acceptable insulin injection sites, including the abdomen, thighs, arms, and buttocks. However, for most people, the best place to inject is the abdomen. The abdomen delivers injected insulin to the body in the most consistent manner, and it is also the most accessible and visible site for most people. An added benefit is that there are relatively few nerve endings in the abdomen, so injections here are often virtually painless — in fact, you may not even feel the needle at all.
No matter where on your body you’re injecting, it is very important to rotate your injection sites. This means not injecting at the same exact location according to a pattern. If you’re using the abdomen as your injection area, two common methods for rotating sites are the curve or “S” method and the horizontal or “keyboard” method. Both involve injecting in three rows, each consisting of five or so injection sites. For the curve or “S” method, you alternate the direction of injections in each row (right to left, then left to right, then right to left again), while for the horizontal or “keyboard” method, each row receives injections in the same direction. When using the arms, thighs, or buttocks as your injection area, the “clock” method is often a better option. This method involves changing sites in a circular pattern of eight or so injections.
When injecting into the abdomen, each injection should be at least two inches away from the navel (belly button) and 1/2 inch away from the previous injection site. Injecting into the same site repeatedly increases the risk of developing lipohypertrophy, or hard, rubbery lumps of fat tissue near insulin injection sites. If a lump is present, it is very important not to inject into it, because the insulin will not be absorbed properly. If you’ve been regularly injecting into areas of lipohypertrophy and have achieved good blood glucose control, you’re almost certainly using more insulin than you’d need if you were injecting into normal tissue. If you were to switch to injecting into an area without lipohypertrophy without reducing your insulin dose, you could experience dangerously low blood glucose as a result. If you’re not sure whether you have lipohypertrophy, stop injecting into the area in question and have it examined by your health-care provider.
As noted earlier, it is important to inject into the subcutaneous layer (just under the skin), not deeper into the muscle. If the needle is too long and insulin is injected into the muscle, it will be absorbed more quickly by the body. This is because muscle tissue has greater blood flow than fat tissue, and exercising muscles, through activities like walking, running, or lifting weights, increases blood flow even more. If insulin is accidentally injected into muscle and then you exercise, you could experience dangerously low blood glucose.
If you are using a needle longer than 5 millimeters, you will need to pinch the skin while injecting to make sure that the insulin enters the subcutaneous layer and not the muscle underneath. You don’t need to pinch while using a 4- or 5-millimeter needle unless you’re injecting into a young child. Although the thickness of their skin is similar to that of adults, children and adolescents have less subcutaneous fat and are therefore more likely to have needles reach their muscle. It is important to always pinch the skin when giving injections to children less than 18 years old if thin, but especially those that are younger than 6 years old even when using the shortest needles.
Most insulin that people with diabetes inject is known as U-100 insulin. This means that there are 100 units of insulin in every milliliter of the liquid. Some people, however — those who are very resistant to insulin and require more than 200 units each day — may instead use U-500 insulin. U-500 insulin is five times as potent as U-100 insulin, with 500 units in each milliliter of the liquid. As you can imagine, the risk of making an error with U-500 insulin is potentially much greater than with U-100 insulin.
U-500 insulin is only available in vials, which means that a syringe must be used. Insulin syringes, however, are designed for U-100 insulin; their markings are wrong for U-500. To avoid accidentally injecting too much insulin when using U-500, using tuberculin syringes is recommended. Tuberculin syringes measure insulin in volume (milliliters) instead of units. Using this type of syringe is a good option for people who might otherwise forget that, when using an insulin syringe, the amount of insulin in the syringe is actually five times the number of units displayed.
Despite this potential safety risk (injecting five times as much insulin as necessary could be deadly), there are health-care providers who instruct their patients to use regular U-100 syringes with U-500 insulin. In this case, extreme caution and proper education are necessary to make sure that people are correctly measuring their insulin doses and understand what each unit marking on the syringe actually means for a dose.
Syringes and pen needles should ideally be disposed of in a sharps container, puncture-resistant containers that are sold in a variety of sizes. Some communities also allow disposal of sharps in a heavy-duty plastic container such as an emptied laundry detergent bottle. To avoid injuring yourself and others, never put loose needles in the trash. Check with your city or town for instructions about how to dispose of sharps containers.
It is important to dispose of pen needles and syringes immediately after using them. Using a needle just one time results in reduced lubrication of the needle surface, which can make injections more painful and increases your risk of developing lipohypertrophy if reused.
If anything in this article has made you question your current injection products or practices, discuss your concerns with your health-care provider. Your provider can help you switch to using shorter or thinner needles if the ones you use now are longer or thicker than necessary. He or she may also be able to advise you about which brand of pen needle or syringe to use; some pen needles are compatible with all pens, while others work only with devices made by the same manufacturer.
No one loves giving insulin injections, but the more you know about injection tools and techniques, the better able you are to take control of your diabetes management and minimize the hassle, discomfort, and possible confusion surrounding injections. More information about injections is available from the American Association of Diabetes Educators here. Whether you’re new to insulin injections or a longtime veteran, take a moment to evaluate your equipment and methods, and raise any concerns or questions with your health-care provider at your next appointment. Your body will thank you for it!
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