What are the common sites for insulin injection?

Common Sites for Insulin Injection

The four recommended sites for subcutaneous insulin injection are the abdomen, thighs, buttocks, and upper arms, with specific anatomical boundaries to ensure safe and effective insulin delivery. 1

Specific Anatomical Boundaries for Each Site

Abdomen (Preferred Site)

• Inject 2 adult fingerbreadths (approximately 1 cm) away from the umbilicus 1
• Stay approximately 1 cm above the symphysis pubis 1
• Stay approximately 1 cm below the lowest rib 1
• Extend laterally to the flanks 1
• The abdomen provides the fastest and most consistent insulin absorption 2

Thighs

• Use the upper third anterior lateral aspect of both thighs 1, 3
• Avoid the inner thigh near major vessels, though recent evidence suggests the upper inner thigh may be acceptable with 4-mm needles 4
• The thigh has the highest risk of intramuscular injection, particularly in lean individuals 5
• Absorption from the thigh is slower than from the abdomen 2

Buttocks

• Inject into the posterior lateral aspect of both upper buttocks and flanks 1, 3
• This site has the slowest insulin absorption rate 2
• Provides the greatest distance from skin to muscle (median 16.9 mm), reducing intramuscular injection risk 5

Upper Arms

• Use the middle third posterior aspect of the upper arm 1, 3
• This site may be difficult for self-injection and often requires assistance 1
• Absorption rate is intermediate between abdomen and thighs 2

Critical Technical Requirements

Needle Selection and Insertion Angle

• Use 4-mm pen needles inserted at 90° for all adults regardless of age, sex, ethnicity, or BMI 1, 3
• The 4-mm needle dramatically reduces intramuscular injection risk compared to 8-mm needles (0.1% vs 9.7% IM risk in abdomen) 5
• If using needles longer than 4 mm, a correctly lifted skinfold is mandatory to avoid intramuscular injection 1

Site Rotation Strategy

• Divide each injection area into quadrants or halves and rotate systematically within one area before moving to another area 3
• Use one zone/quadrant per week to maintain consistent absorption 3
• Inject at least 1 cm from previous injection sites, rotating in a consistent direction 3, 2
• Systematic rotation prevents lipohypertrophy, which causes unpredictable insulin absorption and increased glucose variability 3, 2

Visual Representation of Injection Sites

FRONT VIEW:
- Abdomen: Large area around navel (avoid 1 cm radius around umbilicus)
- Thighs: Upper third, outer/lateral aspect

BACK VIEW:
- Buttocks: Upper outer quadrants
- Arms: Back of upper arms (middle third)

Critical Pitfalls to Avoid

Avoid Intramuscular Injection

• Intramuscular injection causes unpredictable insulin absorption and frequent unexplained hypoglycemia 1
• Risk is highest in lean patients, when injecting into limbs (especially thighs), and with longer needles 1, 5
• The thigh has the shortest skin-to-muscle distance (median 10.9 mm) and highest IM risk 5

Avoid Lipohypertrophy Areas

• Never inject into areas with lipohypertrophy (lumpy tissue), as this causes slower and unpredictable absorption 2
• All injection sites must be inspected at every visit, or at least annually 3
• Patients should self-inspect sites and distinguish healthy from unhealthy tissue 3

Avoid Rotating Between Different Anatomical Regions Daily

• Rotating between different anatomical regions (arms, abdomen, thighs) on different days increases day-to-day glucose variability 6
• Absorption rates vary significantly by site: abdomen (fastest) > arms > thighs > buttocks (slowest) 2
• Consider using one anatomical region (preferably abdomen) for all injections to reduce glucose variability 6

Additional Safety Considerations

Injection Preparation

• Allow insulin to reach room temperature before injection to reduce pain and prevent lipodystrophy 3, 2
• Clean injection site with alcohol swab and allow to dry completely 2
• Avoid injecting through clothing, as this prevents proper site inspection 2

Post-Injection Technique

• Keep the needle embedded in skin for at least 5-6 seconds after complete insulin delivery, particularly with pens 2, 7
• Do not rub the injection site after withdrawal 7
• Dispose of needles immediately in puncture-resistant containers without recapping 7

Special Populations

• Children and lean adults are at highest risk for intramuscular injection and should use a 2-finger lifted skinfold with 4-mm needles 1
• The skinfold technique is less effective in the thigh than in the abdomen 1