We are pleased to present the second in a three-part series on insulin sponsored by Viatris and written by Amy Hess Fischl, MS, RD, LDN, BC-ADM, CDCES. Content is provided for information only; please consult with your health care provider before making changes to your diabetes management.
In All About Insulin (Part One), we covered the basics of insulin use and the types available. This month we'll discuss how to administer and store insulin.
How is insulin administered?
Many people with diabetes who use insulin self-administer it by injecting it into the skin.
Is there one better needle size for injecting insulin?
Size does count! There are two ways to inject insulin depending upon your prescription. If you are using vials, then the only way to inject is with a syringe. There are plenty to choose from based on how much insulin they hold and the size of the needle. They usually describe syringes in terms of CAPACITY, LENGTH, and GAUGE.
Typical capacity sizes:
- 3/10 cc – holds up to 30 units
- 1/2 cc – holds up to 50 units
- 1 cc – holds up to 100 units
If measuring in half-unit doses, the only syringes that have half-unit increments are 3/10 cc syringes and your prescription must be written specifying they need to be 3/10 cc half-unit increment syringes.
Insulin pens can also be used in place of vials and syringes. If you are injecting insulin via pen, pen needles must be used. Like syringes, they are single-use needles attached to the pens themselves.
Syringes and pens have various needle lengths, described in both metric and imperial, highlighting the length in millimeters and inches and the thickness or gauge. When reading the gauge of a needle, the bigger the number, the smaller the thickness, meaning it may go into the skin with less pain. For example, a 32 gauge needle is approximately 0.23-0.24 mm, the size of a human eyelash.
Typical sizes available and recommended include:
- 4 mm (5/32”) - 31 or 32 gauge, in pen needles only
- 5 mm (3/16”) – 31 gauge, in pen needles only
- 6 mm (15/64”) – 31 or 32 gauge, pen needles and syringes
- 8 mm (5/16”) – 31 gauge, pen needles and syringes
What needle size should I choose, and what technique should I use when injecting?
Some research on injections did illustrate interesting points regarding how to inject and key recommendations on choosing the length and gauge of needles. Early research regarding the size of syringes confirmed that shorter needle lengths, like 6mm, had no detrimental effect on overall glucose management in individuals with higher BMI.1 The average skin thickness across the four most common injection sites, the stomach, thighs, butt, and arms, is only 2.0 to 2.5 mm. Based on this information, it is unnecessary to have a needle much longer than this to inject insulin into the subcutaneous layer safely.2
Also, consensus recommendations for insulin delivery were published by clinicians participating in the Forum for Injection Technique and Therapy: Expert Recommendations (FITTER) workshop conducted in October 2015. FITTER was a series of workshops on insulin delivery, and the recommendations are largely based on the results of the most recent Injection Technique Questionnaire (ITQ) survey conducted in 2014–2015.
The questionnaire and workshop concluded that the 4 mm needle and the 6 mm syringe inserted at a 90-degree angle are long enough to go through the skin and enter the subcutaneous fat with little risk of accidentally injecting into the muscle. (Subcutaneous fat is the best place to inject insulin for consistency in how it should work). The consensus recommendation stated that the 4 mm should be considered the safest pen needle, and the 6 mm should be considered the safest syringe for adults and children regardless of age, sex, ethnicity, or body mass index. For most, the needle should not be inserted at an angle. However, the injection should be given at a 90-degree angle in children and very thin adults once the skin is pinched up. Everyone else can inject without pinching at all.3
What other options are available to deliver insulin?
Inhaled insulin was first approved for use in 2014 and comes in a pre-measured blister pack of powder that is inserted into a reusable inhaler.
Insulin pumps have been used for over 30 years, but we are seeing a sharp increase in use by all people with diabetes taking multiple doses of insulin per day. Pumps use only one type of insulin, rapid-acting or short-acting insulin, and the cartridge, reservoir, or pod is typically filled using vials of insulin. However, those who use less insulin overall may fill them with an insulin pen cartridge or pen.
Outside of the US, there are devices that do not use needles to inject insulin. They are called jet injectors. After placing the device against the skin, a button is pressed, and the insulin is pushed through the skin's pores.4
How Should Insulin Be Stored?
You can keep "current" insulin (a few days or a week's supply) at room temperature to help alleviate injection discomfort. Insulin can usually be stored at room temperature for about a month.
Once in use, insulin pens should also be stored at room temperature. Expiration dates of insulin pens can vary depending upon the type of insulin. For disposable pens, you should discard the entire device when empty or when you reach the expiration date.
Store all extra, unopened insulin in the refrigerator. To maintain a consistent temperature in unopened insulin, you should not store it in the refrigerator's door because opening and closing the fridge frequently can affect the temperature of the insulin.
You can keep open insulin in the refrigerator, but cold insulin can cause pain at the injection site. Also, if you use an insulin pump, cold insulin can lead to bubbles in the tubing, cartridge, reservoir, or pod, leading to future inconsistencies in insulin delivery and elevated glucose levels.
Don't expose insulin to excessive cold or heat. Don't store it in the freezer or in direct sunlight, and do not keep it in your vehicle.
- Schwartz S, Hassman D, Shelmet J, et al. A multicenter, open-label, randomized, two-period crossover trial compar- ing glycemic control, satisfaction, and preference achieved with a 31 gauge x 6 mm needle versus a 29 gauge x 12.7 mm needle in obese patients with diabetes mellitus. Clin Ther. 2004;26(10):1663-1678.
- Gibney MA, Arce CH, Byron KJ, Hirsch LJ. Skin and subcutaneous adipose layer thickness in adults with diabetes at sites used for insulin injections: implications for needle length recommendations. Curr Med Res Opin. 2010;26(6):1519-1530.
- Frid A, Kreugel G, Grassi G, et al. New insulin delivery recommendations. Mayo Clinic Proc 2016;91:1231–1255
Amy Hess Fischl, MS, RD, LDN, BC-ADM, CDCES, is an advanced practice dietitian and diabetes care and education specialist at the University of Chicago within the departments of pediatric and adult endocrinology. She speaks internationally on all diabetes topics, especially meal plan options for type 1 diabetes, insulin pumps, and continuous glucose monitors. She is actively involved in the American Diabetes Association, the Academy of Diabetes Care and Education Specialists, and the Academy of Nutrition and Dietetics, as well as several international groups for diabetes and pre-diabetes. She was named 2018 IL AADE Diabetes Educator of the Year and also received the 2018 Pan Arab Congress on Diabetes Award of Excellence for her contributions to diabetes care and education. Her dream vacation always includes diving with sharks.