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If you've ever hit muscle with a needle, you know the pain. If you've ever injected the right dose of insulin and still found your blood sugar sky high, you might have injected too shallowly and hit skin.
Insulin injections that are too deep or too shallow can really foul up glucose levels. For most injections, the goal is to hit the layer of fat between the skin and the muscle.
Hitting this target involves knowing the thicknesses of your own body layers, whether to pinch up or not, and which needle length to use. The medical community is finding that injection techniques play a significant role in blood sugar control.
In September 1998, Practical Diabetes International reported on the first International Insulin Injection Technique Workshop, where 40 diabetes experts from all over the world gathered in Strasbourg, France. Researchers presented studies on injection techniques and gave some guidelines to make proper techniques easier to understand. Studies and tips from the Strasbourg conference were summarized by Kenneth Strauss, MD, medical director of Becton Dickinson, Europe.
Current Needle Lengths
The two most popular sizes of needles are the 12.7-millimeter (1/2-inch) needle and the smaller size, the 8-millimeter (5/16-inch) needle.
Becton Dickinson recently announced the arrival of a new, shorter needle length, the 5-millimeter pen needle. It is recommended for children and extremely lean adults. Because Americans generally have more padding than others, the 5-millimeter needle is used more widely in Europe than in the United States.
Hitting the Fat
What's beneath the surface of your skin? The areas a needle can hit are as follows (also see Figure 1):
If we were all the same size, we could all use the same needle and the same techniques. But, as we know, every person is different, and a child, a thin adult and an obese adult have varying thicknesses of fat and muscle. Even within these groups, thickness of thigh fat and abdominal fat will differ greatly between men and women.
The Abdomen of a Normal-Weight Adult
Male: skin is about 2 1/2 millimeters thick, fat averages 14 millimeters
Female: skin is about 2 1/2 millimeters thick, fat averages 23 millimeters
The Lateral Thigh of a Normal-Weight Adult
Male: skin is about 2 1/2 millimeters thick, fat about 7 millimeters
Female: skin is about 2 1/2 millimeters thick, fat about 14 millimeters
Among all people with diabetes, however, the goal is to hit the fat layer. Going too deep hits muscle. Injections into the muscle cause pain and the insulin can peak in 15 minutes. Muscular injection occurs when people inject into areas with little fat, like a thin thigh, without pinching up. The only occasion that calls specifically for a muscular injection is when BGs are rapidly rising and you need them to rapidly fall.
On the other hand, going too shallow hits the skin or the subdermal layer, between the skin and fat. The insulin gets lost here, and the dose that actually reaches the rest of the body is much lower than the dose intended. Shooting too shallow can occur from angling too much or using a needle that is too short.
In the beginning, there was only the standard needle length, which is 12.7 millimeters. Then the 8-millimeter needle came along. But to get better control from more choices means knowing which to use.
Dr. Stuart Ross and Rozmin Jamel of Canada presented data at Strasbourg showing that glucose control was not changed significantly in normal-weight type 1 and 2 people when switching from a 12.7- to an 8-millimeter needle.
In obese patients, however, control deteriorated with the 8-millimeter needle because of more insulin leakage.
Becton Dickinson's worldwide medical director, Barry Ginsburg, MD, PhD, recommends that overweight adults use the 12.7-millimeter needle. (Overweight is defined as a body mass index [BMI] of over 27.) When using a 12.7-millimeter needle, says Ginsburg, overweight adults should pinch up.
Dr. Anders Frid of Sweden presented his research on a very common injection site, the navel area, which is the fattest area of the abdomen.
Surprisingly, almost half of the men studied did not have enough abdomen fat to use the standard, 12.7-millimeter needle without a pinch up.
Frid showed that 28 percent of thin women and 44 percent of thin men had less than 12.7 millimeters of fat at the navel. If these people use a 12.7-millimeter needle, they could hit muscle.
Thus, these people should be using an 8-millimeter needle, according to Cindy Onufer, RN, MA, CDE, a clinical nurse specialist at Legacy Good Samaritan Hospital in Portland, Oregon. If they must use the longer needle, they should pinch up.
Frid also studied the upper area of the buttocks, near the lower back, in these same thin people. He concluded that this area has so much fat, never less than 13 millimeters, that there is very little chance of hitting muscle when injecting into the buttocks.
Onufer agrees, although she adds that the upper buttocks is an awkward site for people to reach. She says that because it is a very slow absorption area, it is a good site for bedtime injections, and having your partner perform the shot eliminates an awkward reach.
Even among children, females have more fat than males. Dr. Claire Smith of the United Kingdom measured the distance from skin to muscle tissue in children and adolescents at injection sites.
In the abdomen, the distance from skin to the lining of the abdominal cavity was less than 12.7 millimeters in most of the boys, but only in one of the five girls. Thus, boys who use 12.7-millimeter needles risk injecting into their muscles.
To Pinch or Not to Pinch
The workshop's research led to these statements on pinching up:
A summary of the workshop's guidelines on pinch up versus no pinch up:
Before concluding the Strasbourg workshop, the panel outlined the following points about proper insulin injection technique:
The report on the Strasbourg workshop does stress that these statements "do not as yet have the force of guidelines." People with diabetes should always consult with health care professionals before making care changes.
A New Field of Research
Most experts agree that people with diabetes should determine their BMIs then discuss injection sites and techniques with their health care teams.
The Strasbourg research points out the importance of knowing your own body type and which site is best for every type of insulin. This research, plus advice from a health care team, can lead to more effective insulin injections.
Insulin Absorption Rates
How quickly your body absorbs insulin injections depends on which body part is used.
At the Strasbourg conference, Dr. Allan Vaag of Denmark showed that fast-acting insulin absorbs more slowly from the surface just under the skin if injected in the thigh (50 percent of insulin injected was absorbed after five hours). Vaag noted that it absorbs more quickly in injection sites along the abdomen.
Vaag's research suggests that for pre-or post-meal shots, an abdomen injection with rapid-acting insulin works best.
Speed of Delivery
Unless you're injecting Humalog, which always absorbs at the same rate, your injection site affects how quickly the body absorbs the insulin.
|Injection Site||Absorption Rate|
|Thigh and Arm||slower|
How Much Fat Do You Have?
Use this chart as a guide. Your health care team can help you pinpoint good techniques, given your body type.
Although some skin areas are thicker than others, the typical thickness of the skin layer is about 2 1/2 millimeters. Based on research by Frid and Smith:
|Average Thickness of Fat Layer|
|Female Abdomen||23 millimeters|
|Female Thigh||14 millimeters|
|Male Abdomen||14 millimeters|
|Male Thigh||7 millimeters|
Fat layers are thicker than those of normal-weight adults.
Most girls studied had more than 12 millimeters of fat in their abdomen and thigh areas.
Most boys had less than 12.7 millimeters of fat in the abdomen and thigh, indicating that if boys use a 12.7-millimeter needle, they risk injecting insulin into the abdominal cavity or muscle.
Am I "Normal" Weight?
You're not obese, but you're not a marathon runner, either. You're a thin person but your belly, or maybe your thighs, have gotten bigger as you've gotten older. The research says to pinch up when you're doing an abdomen shot, but you're sure you have enough of a belly to avoid hitting muscle. Are you "normal weight," according to the experts' definition?
The definitions have not changed, but people have changed, says Dr. Kenneth Strauss, Becton Dickinson's European medical director, who compiled the information from the Strasbourg conference.
"The definitions for thinness (BMI<19), normal weight (BMI 19-25), mild obesity (BMI 25-27), obesity (BMI) and excessive obesity (BMI>30) are accepted for general adult populations. Though there are slight modifications for children and women, these criteria have not changed over time."
Strauss continues, "What has changed is the percentage of the population occupying each of these categories. People are now heavier than they have ever been since records have been kept on weight. The percentage of persons who are in the three obese categories has grown and even the mean weight of normal-weight adults has increased."
There can be no blanket recommendation covering all people surrounding the normal-weight category, says Strauss. "There will be many who will have enough fat to cover them, but there will equally be many who will inject inadvertently into muscle," he says.
A health care professional who knows your body type well can help give guidelines to the best injection techniques.
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