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Shorter (5-mm) Needles Deliver Insulin Reliably

Aug 20, 2010

New research has found that 5-mm needles effectively deliver insulin into subcutaneous fat in both adults and children. Compared with intramuscular injections of insulin, injections into the subcutaneous fat are associated with less variability in glycemic control as well as a lower risk for hypoglycemia…   

Many factors, including the patient’s body type and the length of the needle, play a role in successfully depositing the insulin into the subcutaneous fat. 

However, little attention has been paid to the role of injection technique in successful insulin injections. An injection performed perpendicularly to the skin with 4-mm needles appears successful in subcutaneous insulin deposition in the majority of lean children and adults. The current study examines injection techniques with 5-mm needles.

According to the researchers, the goal of an injection is to deliver insulin to the subcutaneous fat, but perpendicular insertion of longer needles (i.e., 6-mm, 8-mm, and 12.7-mm) is associated with an increased deposition into the intramuscular layer. Conversely, shorter needles may deliver insulin too superficially into the intradermal layer.

Dr. Paul Leslie Hofman writes,”Our primary aim was to establish the ideal injection techniques required to reliably inject insulin into the subcutaneous fat in both children and adults using 5-mm needles.”

The study included 259 participants, of which 122 were children or adolescents. Each subject was injected with a 32-gauge, 5-mm needle with sterile air, equivalent to 20 units of insulin in volume. Injections into the abdomen and thigh were evaluated when inserted perpendicularly into the skin or at a 45-degree angle and also with or without a pinched skin fold with ultrasound. Test medium injections into the abdomen and thigh were also administered to assess injection leakage.

In children, 5.5% of injections were too deep and were injected into the intramuscular layer, and 0.5% of injections were too shallow, being injected into the intradermal layer. In adults, the incidence was 1.3% and 0.6%, for the intramuscular and intradermal layers, respectively.

The frequency of intramuscular injections was highest in boys and was nearly absent in adult women. Increased thickness of subcutaneous fat was associated with a decreased risk for intramuscular injections (P < .001).

One third of patients had no pain during insulin injection, whereas children and adolescents tended to experience more pain than adults. Injection leakage was unrelated to injection volume and was typically negligible.

“This study has demonstrated that 32G [gauge] 5-mm needles can be reliably inserted into subcutaneous fat, are relatively pain free, and are associated with minimal leakage from the injection site,” the study authors conclude. They also recommend an “angled injection with a pinched skin fold for children, while in adults the technique should be left to patient preference.”

“These findings support the use of 5-mm needles in all patients,” said independent commentator Sherwyn L. Schwartz, MD, with Diabetes and Glandular Disease Research Associates in San Antonio, Texas.

According to Dr. Schwartz, currently available studies on needle length indicate that glucose control is not significantly different when a shorter needle is used in obese patients. “Patients prefer a shorter needle length, and insulin can be delivered to the subcutaneous fat using the proper angle with a 5-mm needle,” Dr Schwartz wrote.

According to Dr. Schwartz, the angle at which the 5-mm needle is inserted is important, depending on how much subcutaneous fat is available. “If the patient is obese, a 90° insertion with a 5-mm needle will get insulin into the subcutaneous fat. With children or thin adults with very little subcutaneous fat, a 45° insertion may be more appropriate,” he said.

Dr. Schwartz noted that other factors that should be considered when selecting needle length are the patient’s physical limitations. “Patients who have ample subcutaneous fat but physical limitations such as tremors may have a difficult time keeping a shorter needle under the skin long enough to inject the complete dose,” he said.

Practice Pearls:
  • The current study suggests that pinching the skin and injecting at a 45-degree angle are effective means to reduce the risk for intramuscular injection of insulin among children being injected with a 5-mm needle.
  • The current study suggests that the risk for intramuscular injection of insulin via a 5-mm needle is lower in adults vs. children, and adults can choose their preferred injection technique.

Diabetes Care. Published online June 28, 2010.