Objective – We aimed to establish the ideal injection techniques using 5-mm needles to reliably inject insulin into the subcutaneous fat in both children and adults, and to quantify the associated pain and leakage of test medium.

Research design and methods – 259 subjects (122 children/adolescents and 137 adults) were injected sterile air corresponding to 20 IU of insulin (200 μl) with 32G 5-mm needles at 90° or 45°, in abdomen and thigh, and with or without a pinched skin fold. Injection depth was assessed via ultrasonography. Subjects rated pain on a visual analog scale. Test medium injections into the abdomen and thigh (0.2-0.6ml) was also administered to assess injection leakage.

Results – Among children, 5.5% of injections were intramuscular (IM) and 0.5% intradermal, while in adults the incidence was 1.3% and 0.6%, respectively. The frequency of IM injections was greater in boys, and negligible among adult women. Subcutaneous fat thickness was the primary predictor of the likelihood of IM injections (p<0.001). A third of all patients reported experiencing no pain during insulin injection, with children/adolescents experiencing considerably more discomfort than adults. Some leakage of medium was observed, but was unrelated to injection volume and was generally minimal.

Conclusions – 5-mm needles are reliably inserted into subcutaneous fat in both adults and children. These needles were associated with reduced pain and minimal leakage. We recommend an angled injection with a pinched skin fold for children, while in adults the technique should be left to patient preference.