The authors aimed to evaluate the pain associated with subcutaneous injection into the thigh and abdomen of different combinations of injection speeds and volumes.

Subcutaneous (applied under the skin) injection of insulin for diabetes control can be associated with pain and discomfort, leading to inadequate treatment adherence or even abandoning the treatment. It is therefore important to understand the injection process to make injections as smooth and painless as possible.

It remains unclear if simple measures, such as using a particular injection site or injection speed and/or volume, could minimize discomfort and pain of injections. The primary objective of this trial, therefore, was to assess and describe pain in relation to injection into the abdomen and thigh of different combinations of injection speeds and injection volumes.

82 patients with type 1 or type 2 diabetes were evaluated. Patients received a total of 17 injections each (12 in the abdomen and 5 in the thigh) at different injection speeds (150, 300 and 450 μl/s) and different volumes (400, 800, 1200 and 1600 μl) as well as 2 needle insertions (1 in the abdomen, 1 in the thigh) without any injection.

Pain scores for most injections were at the lower end of the 0-100 Visual Analogue Scale (a method of measuring pain in adults). Speed of injection had no impact on patient perception of injection pain. Injection of larger volumes (1200 and 1600 μl) was associated with higher perception of pain than lower volumes. Significantly more pain was recorded for 1200 μl compared to both 400 and 800 μl. Likewise, significantly more pain was recorded for 1600μl compared to 1200, 800 and 400 μl. Injections of 400 and 800 μl were associated with pain levels similar to simple needle insertions (placing the needle without injecting fluid).

91.8% of injections administered to the abdomen were rated as acceptable compared to 79.4% of those administered to the thigh. This meant that the odds of an acceptable pain level were 3.7 times higher for injections in the abdomen compared to the thigh. 15.9% of the patients felt that needle insertion in the thigh alone registered as unacceptable pain, while 7.3% of patients felt similarly for abdominal needle insertions.

The authors stated that higher injection volumes and injections in the thighs were associated with higher pain levels than lower injection volumes and injections in the abdomen.

The results of the trial tell us nothing about the relative pain of subcutaneous injection into other sites.