An insulin syringe has four parts: a cap, a needle, a barrel, and a plunger.
- The needle is short and thin and covered with a fine layer of silicone to allow it to pass through the skin easily. A cap covers and protects the needle before it is used.
- The barrel is the long, thin chamber that holds the insulin. The barrel is marked with lines to measure the number of insulin units.
- The plunger is a long, thin rod that fits snugly inside the barrel of the syringe. It easily slides up and down to push the insulin out through the needle. The plunger has a rubber seal on the end that is inside the barrel, to prevent leakage. To measure the required amount of insulin, you move the rubber seal until it matches the correct line on the barrel.
Insulin syringes are made in several sizes.
| Syringe size | Number of units the syringe holds |
|---|---|
|
1/4 mL or 0.25 mL |
25 |
|
1/3 mL or 0.33 mL |
30 |
|
1/2 mL or 0.50 mL |
50 |
Use the smallest syringe size you can for the dose of insulin you need. The measuring lines on the barrel of small syringes are farther apart and easier to see. When you choose the size of syringe, consider the number of units you need to give and how well you can read the numbers on the barrel. A 0.25 mL or 0.33 mL syringe often is best for people who have poor eyesight, because the numbers on the barrel are larger and easier to see.
Lois Jovanovic, MD - Endocrinology
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