Do I Need a Longer Insulin Needle?
I have been injecting insulin for two years. My question is about needle length. I’ve used a U-100 31-gauge, 8-mm “short” needle because—well, it should hurt less, right? Because I am slightly obese, should I use the 29-gauge, 12.7-mm needle instead? Sue Chenoweth, National City, Michigan
Christy L. Parkin, MSN, RN, CDE, responds:
Your question is a common one. As technology improved and shorter needles became available, it was thought that longer needles were still necessary for those who were overweight. Recent research has shown, however, that shorter needles are very effective in delivering insulin into the tissue just under the skin of both lean and overweight people.
What to Know
In just 25 years, we have gone from using 16-mm-long needles that were much thicker in diameter to 4- to 8-mm needles that are very thin (and practically pain-free). But do shorter needles work as well in people with more body fat? Yes, they do. Recent studies using ultrasound to measure skin thickness at four different sites on the body showed there is minimal variation in skin thickness regardless of a person’s age, gender, race, or body mass.
Most people have a skin thickness of less than 2.8 mm, which means that even shorter 4- or 5-mm needles will penetrate the skin and reach the subcutaneous tissue. If insulin is injected with a longer needle (over 8 mm), the chance of injecting into intramuscular tissue is greater. That causes more pain and variation in insulin uptake (and thus in blood glucose levels). The width, or gauge, of a needle has more to do with pain than does the length.
No matter which size needle you use, injection technique is important. With shorter needles (4 to 5 mm), inject at a 90-degree angle with no pinching of the skin. If longer needles are used, pinch up the skin to avoid injecting into intramuscular tissue. Also, hold the needle in the skin for 5 to 10 seconds after you give the insulin (even longer with higher doses) so the medication doesn’t leak from the site. For very lean people, pinching the skin and injecting at an angle are recommended even with shorter needles.
New clinical recommendations support the use of shorter needles. A 4- or 5-mm needle is effective for all body types. The needles are long enough to penetrate the skin into the fat layer but short enough not to reach muscle.