What Size Insulin Syringe Should You Buy?

Diabetes Care

Did You Know?

In most parts of United States, you don’t need a doctor’s prescription to purchase just one insulin syringe.

An insulin syringe is a device that is used to administer the prescribed insulin dose intravenously. The syringe consists of 3 parts, namely the barrel, plunger, and the tip. The barrel is a hollow cylindrical tube, through which the removable plunger (piston-type rod) can be inserted and pulled out. The tip is used for fitting the needle. The plunger helps to draw and push out the contents in the barrel, which are eventually injected into the body through the needle.

When it comes to buying an insulin syringe, it all depends on the amount of insulin that is to be administered daily to control diabetes. To put it simply, your insulin dose dictates the size of your insulin syringe. The syringe should allow you to administer the prescribed dose easily. Buying an insulin syringe that cannot accommodate your dose is wasting money and time.

Choosing the Right Insulin Syringe Size
Insulin syringes come in different sizes, and you need to select one that is appropriate to your dose. Once you know your exact prescribed dose, here is what should be considered when buying a syringe.

Barrel Size
The barrel size determines the maximum capacity of insulin that the syringe can hold. Knowing the barrel size will give you an idea about the amount of insulin that can be drawn into the syringe. As aforementioned, the barrel refers to the cylindrical body of the syringe that holds the required dose. Usually made up of plastic, the barrel is calibrated with graduation marks (lines) that enable you to measure the volume of insulin in milliliters (mL) or cubic centimeters (cc)

The different sizes of syringes are discussed below:

  • A 100-unit syringe (commonly referred to as U-100) has the capacity to accommodate 100 units of insulin in a volume of 1 mL or 1 cc. The term U-100 signifies the concentration of insulin present in every 1 mL. The dose is diluted in such a way that 1 mL of fluid will contain 100 standard ‘units’ of insulin. Every line marked on a 100-unit syringe signifies 2 units of insulin.
  • A 50-unit syringe has the capacity to accommodate 50 units of insulin in a volume of 1/2 mL or 0.5 cc. Every line marked on a 50-unit syringe signifies 1 unit of insulin.
  • A 30-unit syringe has the capacity to accommodate 30 units of insulin in a volume of 3/10 mL or 0.3 cc. Every line marked on a 30-unit syringe signifies 1 unit of insulin.

If your insulin dose is below 30 units at a time, choosing a 30-unit syringe is appropriate. In case, your insulin dose lies between 31 and 50 units at a time, you can purchase the 50-unit syringe. Patients who are taking insulin dose that varies from 51 to 100 units, should purchase 100-unit syringe.

Diabetes in early stages may require miniscule amounts of insulin (such as 1/2 unit of insulin) or in some cases, the dose prescribed cannot be rounded to the nearest whole number (for instance 4 1/2 units). For such accurate measurements, you need to buy syringes etched with 1/2 unit markings. Doctors often recommend small capacity syringes when it comes to calculating doses in half units. A 30-unit syringe comes with half-unit markings and can certainly help to measure small doses.

General Rule of Thumb
The syringe should be big enough to comfortably accommodate the entire prescribed dose of insulin. As a general rule of thumb, buy a syringe whose barrel size is significantly larger than the required dose. For instance, if your doctor has prescribed 49 units of insulin and you go for 50-unit syringe, it will be rendered useless if your dose gets revised to 52 units. In such cases, it is always better to buy a 100-unit syringe. So, make sure that your daily dose is never equivalent or near the maximum amount of insulin the syringe can hold. All in all, buy the next size insulin syringe whenever the dose is close to the maximum volume of insulin the syringe can accommodate.

Another reason why you should not utilize the full capacity of the syringe is because there is a high probability that the plunger may not fit properly and get pushed out when administering the medicine.

In order to ensure that the correct dose is administered, it is of prime importance that you are able to identify the etched markings on the syringe. Difficulty in reading the markings can lead to the wrong dose being administered, which can eventually have a negative impact on your health. Measuring the dose in a lower capacity syringe is found to be simpler and chances of any error are minimal. However, you need to ensure that smaller capacity syringes cater to your daily insulin dose.

Needle Length
Once, you have chosen the right insulin syringe size, does the length of the needle matter? Scientific data suggests that needle length plays a critical role in alleviating pain associated with injecting insulin. Studies show that lesser the length of the needle, lesser will be the discomfort when administering insulin. Also, as long as the right method is used to inject insulin, the length of the needle does not matter when it comes to managing glucose levels effectively. Health care professionals recommend a shorter needle length of 6 or 8 mm for better pain acceptance and to prevent any sort of muscle injuries.

Needle Gauge
The term ‘gauge’ refers to the thickness of the needle and can be anywhere between 28 gauge and 31 gauge. Higher the gauge number, lesser will be the thickness of needle. For instance, a 31 gauge needle is thinner than a 30 gauge needle. Pain tends to be more when using 27 and 28 gauge needles through the skin in comparison to 31 gauge needles. So, choosing thinner needles may reduce your chances of having a painful experience from injecting insulin.


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