Insulin Pen Injection Sites
Inject insulin into the abdomen (2 fingerbreadths from the umbilicus), upper third of the thighs (anterior lateral aspect), buttocks (posterior lateral aspect), or middle third of the upper arms (posterior aspect), using a 4-mm pen needle inserted at 90° for all adults regardless of body size. 1
Recommended Injection Sites
The four approved body areas for insulin injection are:
- Abdomen: Inject 2 adult fingerbreadths (approximately 1 cm) away from the umbilicus, staying at least 1 cm above the pubic bone and 1 cm below the lowest rib, extending laterally to the flanks 1, 2
- Thighs: Use the upper third anterior lateral aspect of both thighs 1
- Buttocks: Inject into the posterior lateral aspect of both upper buttocks and flanks 1
- Upper arms: Use the middle third posterior aspect of the upper arm 1
The abdomen provides the fastest and most consistent insulin absorption, making it the preferred site for most patients 2. The arm is the least preferred site for self-injection because it may be difficult to maintain the optimal 90° angle or perform a skin lift independently 1.
Proper Needle Technique
Use 4-mm pen needles inserted perpendicular (90°) to the skin surface for all adults regardless of age, sex, ethnicity, or BMI 1. This needle length is sufficient to reliably deliver insulin into the subcutaneous tissue while minimizing the risk of painful intramuscular injection 1. Research demonstrates that 8-mm needles carry a 25% risk of intramuscular injection in the thigh and 9.7% in the abdomen, compared to only 1.6% and 0.1% respectively with 4-mm needles 3.
If you must use needles longer than 4 mm, you must perform a correctly lifted skinfold to avoid intramuscular injection 1. A 5-mm needle is an acceptable alternative if 4-mm needles are unavailable 1.
Critical Site Rotation Strategy
Divide each injection area into quadrants or halves and rotate systematically within one area before moving to another area, injecting at least 1 cm from previous injection sites 2, 4. For example, use one zone/quadrant per week 4. This systematic rotation prevents lipohypertrophy (lumpy, thickened tissue), which causes unpredictable insulin absorption and increased glucose variability 2, 4.
Never inject into areas with lipohypertrophy, scars, stretch marks, tattoos, or skin that is tender, bruised, inflamed, or damaged 1. Avoid bony prominences by 1 to 2 adult fingerbreadths 1.
Special Populations Requiring Skin Lift
Certain patients are at higher risk for accidental intramuscular injection and should use a 2-finger lifted skinfold technique even with 4-mm needles 1:
- Children and lean adults (BMI <19 kg/m²) have shorter distances between skin and muscle 1, 2
- Older adults may have thinner skin, though this should be assessed individually 1
- Pregnant women should use lateral abdominal areas or implement a skin lift in central areas during the 2nd and 3rd trimesters 1
The skinfold technique is much less effective in the thigh than in the abdomen for preventing intramuscular injection 1.
Injection Technique Details
Allow insulin to reach room temperature before injection by leaving it out of the refrigerator for 30-60 minutes, as cold insulin is more painful and may contribute to lipodystrophy 1, 5, 6. Clean the injection site with an alcohol swab and allow it to dry completely 1, 6.
After inserting the needle fully and pressing the injection button completely, wait at least 10 seconds before removing the needle from the skin to reduce insulin leakage 1. Remove the needle immediately after each injection to prevent air accumulation in the cartridge, which can cause serious underdosing 7.
Common Pitfalls to Avoid
Accidental intramuscular injection in the thigh increases insulin absorption by at least 50%, causing unpredictable effects and potential hypoglycemia 8. This risk is highest at the thigh compared to other sites 3, 8.
Never inject through clothing, as this prevents proper site examination, skin lift technique, and verification of needle penetration 1. Do not reuse needles, as this increases the risk of wrong dosing and infection 5, 6.
All injection sites must be inspected at every regular visit, or at least annually, to screen for lipohypertrophy and other complications 1, 2, 4.