How to Read a U-100 Syringe

Written by sarah mcleod
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How to Read a U-100 Syringe
Needle size determines the gauging of insulin syringes. (needle invert image by Sly from

Used for the treatment of diabetes by injectable insulin, U-100 syringes can hold up to 100 millilitres of fluid. Every millilitre is defined as a unit. These syringes are numbered in increments of 10 making volumes of 10, 20 and incrementally successive integers easy to read. Graduated line markings on the syringe barrels vary, depending on the size or gauge of the needle. Larger, 31-gauge needles tend to measure the smallest amounts of insulin in increments of 2 units. Graduated lines on smaller needle syringes measure one unit per line. Smaller needles are designed for smaller insulin doses.

Skill level:
Moderately Easy


  1. 1

    Ask your health care provider or local pharmacist to adequately explain the kind of U-100 syringe that is best suited to meet your prescribed insulin needs. The manufacturer is not as important to know as the needle gauge size. The needle gauge size determines the increment levels. Knowing your syringe increment level is essential to measuring the amount of insulin that will be needed at each injection. Specifically, make sure your provider or pharmacist explains if every graduated line on the syringe barrel equals one or two units. Over- or under-dosing can result in life-threatening body reactions.

  2. 2

    Obtain a syringe reference guide from your pharmacist. Keep it nearby in case you have trouble remembering what each graduated line represents on your syringe barrel. Insert the U-100 syringe needle into the insulin medication vial. Suspend the needle in the fluid and pull the plunger back until the desired amount of insulin is suctioned up into the syringe. For insulin amounts prescribed in multiples of 10, simply fill the syringe up to the numbered marking. This is the easiest way to read a U-100 syringe. For prescribed insulin amounts in numbered intervals that are not multiples of 10, reading your syringe can get a little tricky.

  3. 3

    Recall your U-100 syringe increment level. If you need 35 units of insulin and your increment level is one, make sure to fill your syringe up to five unnumbered lines above the number 30. This exact measurement will be a bit harder to make with a syringe incremented in units of two but the same method should be followed. Should you accidentally pull back too much insulin into your U-100 syringe, simply pull the needle out of the insulin vial and shoot out the excess with the plunger.

Tips and warnings

  • To prevent dosing mistakes, syringe manufacturers have developed different sizes for varying patient needs. Physicians and pharmacists are educated on available syringe sizes and their corresponding increment levels. They will recommend the syringe that will be easier for you to use based on your insulin prescription.

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