Skin and subcutaneous adipose layer thickness in adults with diabetes at sites used for insulin injections: implications for needle length recommendations

Objective: During subcutaneous insulin therapy, inadvertent intramuscular (IM) injections may increase pain and/or adversely affect glucose control. The most appropriate needle length for patients depends on skin thickness (ST) and the distance to muscle fascia. ST and subcutaneous adipose layer thickness (SCT) were measured in adults with diabetes. Research design and methods: A total of 388 US adults with diabetes (in three BMI subgroups: <25, 25-29.9, and >= 30 kg/m(2)) with diverse demographic features were evaluated. Each subject had ultrasound measurements of ST and SCT at four injection sites. Results: Subjects had BMI 19.4-64.5 kg/m(2), age 18-85 years; 40% Caucasian, 25% Asian, 16% Black, 14% Hispanic; 28% type 1 diabetes. Mean ST (+/- 95% CI) was: arm 2.2 mm (2.2, 2.3), thigh 1.9 mm (1.8, 1.9), abdomen 2.2 mm (2.1, 2.2) and buttocks 2.4 mm (2.4, 2.5). Multivariate analyses showed body site, gender, BMI, and race are statistically significant factors for ST but effects were small. Thigh ST was <0.6 mm thinner than the buttocks. Differences of 10 kg/m(2) account for 0.2 mm ST variation. Mean SCT was: arm 10.8 mm (10.2, 11.3), thigh 10.4 mm (9.8, 10.9), abdomen 13.9 mm (13.2, 17.7) and buttocks 15.4 mm (14.7, 16.2). Females had 5.1 mm greater SCT. Differences of 10 kg/m(2) account for 4 mm SCT variation. Adverse events: A few mild hypo- or hyperglycemia events, unrelated to study procedure, were detected and treated before subject discharge from study visits. Limitations: Only adults in the US were studied; some measurements could not be obtained on every subject, at every injection site. Conclusions: Injection site ST does not differ by clinically significant degrees in demographically diverse adults with diabetes; SCT has a wider range. Needles >= 8 mm, inserted perpendicularly, may frequently enter muscle in limbs of males and those with BMI <25 kg/m(2). With 90 degrees insertion, needles 4-5 mm enter the subcutaneous tissue with minimal risk of IM injection in virtually all adults. These data will assist recommending appropriate length needles for subcutaneous insulin injections in adults.