What size insulin pen needles should I purchase for insulin (intramuscular injection) therapy?

From the Guidelines

For insulin pen needles, I recommend using 4-mm length needles, as they are safe, effective, and less painful for all adults, regardless of age, sex, ethnicity, or BMI, as supported by the most recent study 1. When purchasing, look for needles compatible with your specific insulin pen brand. The needle gauge (G) indicates thickness—higher numbers mean thinner needles, with 31G-32G providing a good balance between comfort and durability. Some key points to consider:

• 4-mm pen needles are recommended for all adults, as they reduce the risk of injecting into muscle and are generally comfortable and effective 1.
• If 4-mm pen needles are unavailable, 5-mm needles can be used as a backup option, but longer pen needle lengths of 6 to 8 mm should be discouraged due to the higher risk of intramuscular injection 1.
• Healthcare professionals should discuss the pros and cons of various needle lengths with the individual patient to arrive at an appropriate personalized decision 1. Always dispose of needles properly in a sharps container after single use to prevent infection and maintain injection comfort. Consult your healthcare provider if you experience pain or leakage during injections, as they may recommend adjusting your needle size.

From the Research

Insulin Pen Needle Size Selection

The selection of insulin pen needle size is crucial to ensure proper insulin delivery and minimize the risk of intramuscular (IM) injection. Several studies have investigated the optimal needle length for subcutaneous insulin therapy.

• A study published in 2014 2 measured the distance from skin to muscle at various injection sites and found that the median distance ranged from 10.9 mm at the thigh to 16.9 mm at the buttock. The study suggested that shorter needles (4 mm) can reduce the risk of IM injection, especially in patients with higher body mass index (BMI).
• Another study published in 2015 3 discussed the importance of considering non-traditional factors, such as patient circumstances and comorbid conditions, when selecting needle length. The study noted that 4-mm pen needles are efficacious in all patients, regardless of BMI.
• A clinical trial published in 2010 4 compared the safety and efficacy of a new 4 mm x 32G insulin pen needle with 5 mm and 8 mm needles. The study found that the 4 mm needle provided equivalent glycemic control with reduced pain and was preferred by patients.

Factors Influencing Needle Length Selection

Several factors can influence the selection of insulin pen needle length, including:

• Body mass index (BMI): Studies have shown that BMI can affect the distance from skin to muscle, with higher BMI individuals requiring longer needles 2, 5.
• Injection site: The distance from skin to muscle varies at different injection sites, with the thigh having the shortest distance 2.
• Patient circumstances: Non-traditional factors, such as physical disability and comorbid conditions, should be considered when selecting needle length 3.

Recommendations

Based on the available evidence, the following recommendations can be made:

• For most patients, a 4 mm or 5 mm needle is sufficient for subcutaneous insulin therapy 2, 4.
• For patients with higher BMI or those who require longer needles, a 6 mm or 8 mm needle may be necessary 2, 5.
• Patients should be assessed individually, taking into account their specific circumstances and comorbid conditions, to determine the optimal needle length 3.