What important instructions should be given to a patient starting insulin therapy regarding subcutaneous injection technique, site rotation, and pen priming?

Insulin Administration: Key Patient Instructions

Patients starting insulin therapy should inject subcutaneously at a 90-degree angle using 4-mm needles, systematically rotate injection sites to prevent lipohypertrophy, and always prime insulin pens before each injection. 1

Correct Injection Technique

Needle Selection and Angle

• Use 4-mm pen needles inserted at 90 degrees for all adults and children, regardless of age, sex, ethnicity, or BMI 1, 2
• This is the safest needle length that reliably delivers insulin to subcutaneous tissue while avoiding painful intramuscular injection 1
• Longer needles (6-8 mm) should be discouraged due to significantly higher risk of intramuscular injection—an 8-mm needle has a 25% intramuscular risk at the thigh versus only 1.6% with a 4-mm needle 3

Special Populations Requiring Modified Technique

• Thin individuals, children, older adults, and pregnant women may need to lift a skinfold when injecting, even with 4-mm needles, to ensure adequate subcutaneous tissue 1, 2
• The skinfold should be lifted gently with thumb and index finger—avoid squeezing tightly enough to cause blanching or pain 1

Critical Importance of Site Rotation

Why Rotation Matters

• Never inject into the same location repeatedly—this causes lipohypertrophy (lumpy tissue buildup) that results in unpredictable insulin absorption and poor glucose control 4, 2, 5
• Lipohypertrophy areas show slower, less predictable absorption and increase glucose variability 2, 6

Proper Rotation Strategy

• Divide each injection area into quadrants and rotate systematically within one area before moving to another 2
• Inject at least 1 cm (approximately 2 fingerbreadths) from previous injection sites 4, 2
• Recommended sites include abdomen (fastest absorption), thighs, buttocks, and upper arms 4, 2
• Stay at least 2 fingerbreadths away from the umbilicus when injecting in the abdomen 2

Insulin Pen Priming Requirements

Mandatory Priming Steps

• All insulin pens must be primed before every injection—this applies to adults and children alike 1
• Priming ensures free and unobstructed insulin flow by verifying at least one drop of insulin appears at the needle tip 1
• This step prevents dose inaccuracy and ensures the full prescribed dose is delivered 1

Additional Pen Use Guidelines

• Do not touch the thumb button until the needle is fully inserted into the skin 1
• Keep pressure on the thumb button and leave the needle embedded in skin for 5 seconds after complete insulin delivery (some guidelines recommend up to 10 seconds) 1, 4
• Remove the needle immediately after injection and dispose of it—never leave needles attached to pens, as this allows air contamination and medication leakage 1

Insulin Preparation

Temperature Considerations

• Allow refrigerated insulin to reach room temperature (30-60 minutes) before injection 4
• Cold insulin causes more pain and may contribute to lipodystrophy development 4, 2

Cloudy Insulin Resuspension

• For NPH and premixed insulins, gently roll the pen horizontally between palms 10 times, then tip up and down 10 times 1
• Visually confirm crystals are fully dissolved before injecting 1
• Avoid vigorous shaking, which creates air bubbles that affect dose accuracy 1

Site Preparation

• Clean hands and inspect the injection site before each injection 1
• If using alcohol swabs, allow the site to dry completely before injecting 1, 4
• Never inject into areas with lipohypertrophy, inflammation, edema, infection, or ulceration 1, 4

Common Pitfalls to Avoid

Why NOT to Inject Intramuscularly

• Intramuscular injection is dangerous—it causes unpredictable, faster insulin absorption leading to unexpected hypoglycemia and poor glucose control 5, 3
• This is why subcutaneous injection at 90 degrees with short needles is essential 1

Why NOT to Use the Same Location

• Repeatedly injecting the same spot creates lipohypertrophy, which paradoxically causes slower and erratic insulin absorption 2, 6
• Patients often continue using these areas because they become less painful over time, creating a harmful cycle 6

Other Critical Errors

• Never share insulin pens between patients—this can transmit bloodborne pathogens 1
• Do not reuse pen needles—they are no longer sterile and can become bent or hooked, causing tissue damage 1
• Verify the insulin label before each injection to prevent medication errors 1, 4