Selecting Syringes and Needles
Medically Edited and Reviewed by Dr. Erin Zinkhan MD, BSBE
Most of us are familiar with a syringe, which is a small plastic tube with a needle at one end. Syringes are used for giving medication usually into a vein, muscle, or under the skin. Without the needle, syringes can also be used to give medications orally or into feeding tubes. For many, syringes are one childhood memory that can never be forgotten! But while your early years may have been spent in fear of needles, health problems may require that you use syringes to give yourself or a loved one medication. If you need to use syringes at home, you will need to know how to use them. You will need to know that not all syringes are the same and that specific syringes are used for specific purposes.
Types of Syringes
Syringes are available in several different varieties. Most syringes are disposable. Syringes are available either with or without an attached needle. The volume of medication the syringe can hold determines the size of the syringe you should select. Below are images depicting the anatomy of a syringe and the anatomy of a needle.
The size of syringe you will need is based on the volume of medication to be given and the desired pressure flow. Volumes are usually measured in cubic centimeters (cc) or milliliters (mL). Both measurements are equivalent in volume. A 1 cc syringe is the same as a 1 mL syringe. Large volumes of medication require larger syringe sizes. Lower pressure flows also require larger syringes. The use of the syringe for injections, medical tubing or irrigation are also factors in syringe selection. A very common type of syringe is the U-100 insulin syringe. The U-100 insulin syringe is used commonly for diabetic medications. This syringe is intended for one-time use only. Below is an infographic depicting the size of the syringe matched with the use for the syringe.
A Luer Lock tip syringe is used most commonly. The needle is secured to the syringe by twisting it on. Putting the needle onto the syringe and taking it off the syringe are easy and quick. The twist mount helps secure the needle to the syringe for greater safety.
A needle can be pushed directly onto a slip tip syringe without twisting. A catheter slip tip is used usually with medical tubing like catheters or feeding tubes.
Eccentric tips are best for when you need to inject a medication parallel to the skin of the patient. It is used also when you want to inject into a vein near the surface of the skin.
Catheter syringe tips are made with a tapered tip to allow tubing to slip on to the tip. The catheter syringe often is used for irrigation.
Needles have a hub at one end that attaches to a syringe. The shaft of the needle comes in varying lengths measured in inches. The thickness of the needle is measured by gauge sizes. Higher gauge sizes indicate thinner needles. The tip of the needle typically has a bevel, or a slope, to provide easier passage of the needle into tissue. Many needles come with a cap to protect the caregiver from accidental needle sticks.
There are three main considerations for selecting the most appropriate needle — needle gauge, needle length, and intended use. The needle gauge and length should be appropriate for the type of tissue that the needle needs to go into. The intended use of the needle means that you need to know how deep the needle must go to reach the best injection area and through which tissues the needle must pass to get to the injection area. These injection depths are labeled as intradermal (for dermis injections), subcutaneous (for subcutaneous fat tissue injections), and muscle (for intramuscular injections).
The appropriate needle gauge is one that is best suited to both the type of medication being given and to the location on the body that the needle must pass through. Needle thickness is measured using needle gauges, which are numbers indicating the diameter of the needle. Lower needle gauge numbers indicate a wider needle diameter, and higher needle gauge numbers indicate a narrower needle. Wider gauges allow for thicker medications to be given more easily. Wider gauge needles may need to be used for areas on the body with thicker skin, such as the soles of the feet. The most common needle gauges are 26- and 27-gauge needles. These two gauges can be used with all three types of injections — intradermal, intramuscular, and subcutaneous. See the Needle Gauge continuum below for more details.
Fine gauge needles cause less pain when the needle passes through the skin, while thicker gauges are best for either areas of the body with thick skin or for when a medication is thick. Gauge numbers are arranged so that the highest number indicates a smaller needle width while the lowest number indicates the largest width. Thicker medications therefore would require the use of a wider width needle or a needle with a lower gauge number.
Common needles vary in length from 3/8 inch to 3-1/2 inch. You should select the most appropriate needle length for where the injection needs to be administered. Generally, the deeper the intended depth of the injection, the longer the needle needs to be. Intramuscular injections require the longest needle lengths. Common needle lengths for intramuscular injections are from 7/8 to 1-1/2 inches. Subcutaneous injections usually require needle lengths from 1/2 to 5/8 inches. Intradermal injections require a needle length from 3/8 to 3/4 inch. The 1/2- and 5/8-inch needle lengths are the two most common needle lengths and can be used for both intradermal and subcutaneous injections. Below are three graphics to help select which is the best needle for your needs.
Purchasing Syringes and Needles
When you buy syringes, it is important that you know the most suitable syringe for your needs. How much medication are you giving to the patient with each injection? Are you using the syringe with a needle for intradermal injections, intramuscular injections, or subcutaneous injections? The needle gauge and needle length selections differ depending on the type of injection. See the Needle Selection Continuum for needle gauge and the Needle Selection Continuum for needle length infographics displayed above for more information. Below is a quick list of the selection criteria used for purchasing a syringe and needle.
- Volume of medication to be administered impacts which syringe size should be used.
- Type of needle hub (Luer Lock, Slip Tip, Eccentric Tip, or Catheter Tip) needs to match the correct syringe.
- Thickness of the medication impacts which needle gauge should be used.
- Location of injection on the body impacts which needle gauge and needle length should be used.
Make sure you know your needs prior to shopping!