An insulin pen is a portable medical device that helps people with diabetes inject measured doses of insulin. It combines an insulin cartridge, a dose dial, a plunger mechanism, and a fine needle in one handheld tool. The main advantage is that users can select a dose in insulin units and deliver it accurately without drawing medicine into a syringe.
This makes daily treatment faster, more convenient, and easier to repeat correctly.
Key Facts
- Dose in units is set by rotating the dose dial before injection.
- For U-100 insulin, 100 units = 1 mL, so volume in mL = dose in units / 100.
- A 12 unit dose of U-100 insulin has volume = 12 / 100 = 0.12 mL.
- The plunger moves the cartridge stopper forward, forcing insulin through the needle.
- Priming removes air and confirms insulin flow before the selected dose is injected.
- Needle length and injection angle help place insulin into subcutaneous tissue, not muscle.
Vocabulary
- Insulin pen
- A handheld injection device that stores insulin and delivers a selected dose through a small needle.
- Dose dial
- The rotating control on an insulin pen that lets the user choose the number of insulin units to inject.
- Cartridge
- The small container inside the pen that holds the insulin solution.
- Plunger
- The moving part that pushes on the cartridge stopper to force insulin out through the needle.
- Subcutaneous tissue
- The layer of fatty tissue under the skin where insulin is usually injected for steady absorption.
Common Mistakes to Avoid
- Skipping the prime step: this is wrong because trapped air or a blocked needle can cause less insulin to be delivered than the dial shows.
- Removing the needle immediately after pressing the injection button: this is wrong because some insulin may still be flowing, so the full dose may not enter the tissue.
- Confusing insulin units with milliliters: this is wrong because the pen dial shows units, and the liquid volume depends on insulin concentration such as U-100.
- Reusing a damaged or dull needle: this is wrong because it can increase pain, bend the needle, clog the flow, or affect dose delivery.
Practice Questions
- 1 A student sets a U-100 insulin pen to 18 units. What volume of insulin in milliliters is delivered?
- 2 A pen cartridge contains 3.0 mL of U-100 insulin. How many total units of insulin are in the cartridge?
- 3 Explain why priming an insulin pen before injection improves dose accuracy, even if the dose dial is set correctly.