What Is A Insulin syringe?

An insulin syringe is a sterile, single-use medical device designed for administering insulin to patients with type 1 or type 2 diabetes; it is suitable for both clinical treatment and daily self-care. Although they resemble standard disposable syringes, insulin syringes have simpler specifications and distinctive scale markings that offer great convenience for the daily management of diabetes. This article provides a detailed overview of insulin syringes, covering their structural components, types and specifications, usage instructions, and important precautions.

Components of A Insulin Syringe

Similar to standard syringes, insulin syringe has the following parts (refer to the picture below): barrel, plunger, gasket, needle and needle protective cap. Besides, the insulin syringe with fixed needle has a extra plunger cap.

Barrel

Due to their very small capacities—typically available in sizes such as 1 mL, 0.5 mL, and 0.3 mL—insulin syringes feature exceptionally slender barrels. Therefore, the markings on the barrel are not in milliliters (ml) but in Units (U).

Key point: To facilitate calculations and avoid reading errors, insulin solutions currently intended for human use employ an internationally standardized concentration (the U-100 standard), meaning that every 1 milliliter (mL) of liquid contains 100 units of insulin.

For U-100 specification 1 mL syringes, the maximum injection volume is 100 units insulin. To facilitate patient use, the markings on the syringe barrel indicate dosage units directly rather than volume units (mL). This eliminates the need to convert volume to dosage, allowing patients to read the actual medication dosage intuitively and accurately. For example, if an injection of 55 units of insulin is required, simply draw the insulin solutions up to the 55-unit mark.

Furthermore, for patients requiring smaller doses of insulin (such as only 15 or 35 units per injection), using a 1 mL syringe may increase the risk of dosing inaccuracy due to the narrow spacing between scale markings. Consequently, 0.5 mL and 0.3 mL insulin syringes—which have smaller capacities—were developed to ensure precision and safety when administering low doses.

Needle

Patients with diabetes require frequent, long-term insulin injections; therefore, ultra-fine needles (such as 29G to 32G gauges) are typically used to minimize discomfort. Additionally, insulin syringe needles are shorter than those of standard syringes, usually ranging from 4 mm to 12.7 mm in length. This is because insulin must be injected into the subcutaneous tissue; a needle that is too long could accidentally penetrate the muscle layer, which could lead to blood glucose fluctuations.

Needle Protective Cap

The needle protective cap is designed to reduce the risk of needlestick injuries to users. To facilitate identification by healthcare professionals and diabetics, the cap colors follow international standards: orange caps are used for U-100 syringes, and red caps for U-40 syringes.

Plunger Cap

A plunger cap is a standard component of integrated (fixed-needle) insulin syringes; it protects the plunger and works with the needle protective cap to form a sterile barrier, ensuring the insulin syringe remains sterile as long as both caps remain intact. In contrast, insulin syringes with detachable needles are individual sterile-packaged and feature a more robust plunger, thus eliminating the need for a plunger cap.

Types of Insulin Syringe

U-100 & U-40 insulin syringes

U-100 means it contains 100 units of insulin per milliliter (ml). U-40 means 40 units/ml. Insulin solutions for human injection are typically U-100 concentration; therefore, the syringes used are designed specifically for U-100 insulin and feature an orange needle protective cap. U-40 concentration insulin is rarely used in clinical practice and is primarily intended for pets (such as cats and dogs) requiring small doses. It is characterized by a red protective cap.

Insulin syringes with fixed needles and insulin syringes with detachable needles

Insulin syringes with fixed needles feature protective caps at both ends—covering the needle and the plunger, respectively—to create a sterile barrier; as long as the caps remain intact, the syringe maintains sterility, making it ideal for daily use and portability by diabetic patients. Detachable insulin syringes come in individual sterile packaging and are ready for immediate use, making them an ideal choice for sterile clinical settings in hospital.

Specifications of Insulin Syringe

Syringe Capacity

U-40 and U-100 insulin syringes can be distinguished by the color of their needle protective caps: U-100 syringes have orange caps, while U-40 syringes have red caps. Both types are available in 0.3ml, 0.5ml and 1ml.

Needle Gauge

To minimize injection pain, insulin syringes are typically equipped with ultra-fine needles, such as 29G, 30G and 31G.

Needle Length

Since the insulin is administered into the subcutaneous fat layer, which lies close to the skin’s surface, insulin syringes’ needles are designed to be very short, with lengths generally ranging from 4 to 12.7mm, to prevent penetration into muscle tissue.

How to use insulin syringe

Preparation: insulin syringe, alcohol pad, insulin solution

Before using an insulin syringe, please wash your hands to ensure they are clean.

Check whether the insulin is expired and whether the insulin vial is damaged.

After removing the needle protective cap, draw in an amount of air equal to the required dose of insulin. Then insert the needle into the rubber stopper of the vial and push the syringe plunger to inject air. (This step will help accurately draw up the required dose. Directly withdrawing liquid disrupts the pressure balance within the vial, creating negative pressure; pre-injecting an equal volume of air maintains constant internal pressure, thereby ensuring a smooth withdrawal process.)

Next, invert the insulin vial, insert the syringe from below, and slowly pull the plunger to draw up the required dose of insulin solutions. (If you accidentally draw up too much insulin, do not push the plunger back to return the insulin to the vial; instead, discard the syringe and draw up a fresh dose.)

Before injecting insulin, disinfect the injection site with alcohol pad, allow it to air dry, and then proceed with the injection. (Avoid injecting insulin repeatedly at the same site to prevent lipohypertrophy and lipoatrophy.)

After completing the injection, do not dispose of the used insulin syringe carelessly; place it in a collection container and then hand it over to a nearby hospital or clinic for proper disposal.

Precautions For Use

Double-check before injection

Before injection, be sure to confirm that the insulin solution is within its expiration date, that the insulin vial is intact and the insulin syringe is undamaged.

Select the correct model of insulin syringe

Be sure to select a syringe that matches the insulin concentration; otherwise, it will overdose or underdose that may be cause blood sugar problems.

For example, if you are supposed to inject 30 units insulin but use the 1ml syringe which matches U-40 to draw in U-100 insulin solution; then you will find you overdose, since the 30 units in U-40 syringe means 0.75ml, 0.75ml U-100 means 75 units insulin.

Don’t reuse the insulin syringe

The used insulin syringes are no longer sterile and can easily become contaminated with dust; reusing them greatly increase the risk of infection. Therefore, do not reuse the insulin syringe.

Don’t wipe the syringe needle with alcohol

Insulin syringe needles are often coated with silicone to reduce penetration resistance and alleviate pain. Alcohol, however, can remove this silicone coating, causing the needle to become dull.

Don’t inject multiple times at the same site

Repeated injections of insulin into the same site can easily lead to subcutaneous fat hypertrophy. Consistently rotating injection sites in areas such as the abdomen, thighs, and upper arms can significantly reduce the occurrence of this issue.