Unlike standard measurement systems, there is an inverse relationship for the gauge numbers and the size of needles. As the gauge number increases, the needle width gets narrower. For example, a 22g needle is thinner than a 21g. This difference is critical to remember, as there is no uniform gauge size for all phlebotomist patients. Each needle varies in their blood flow rate and compatibility with specific vein types.
Although 21, 22, and 23 gauge needles are three of the most common needles, a broad knowledge of all needle types is beneficial to accommodate the different sizes of veins and tissues the phlebotomist may come across.
18 Gauge Needles
18g needles are not used for routine blood draws. A needle this large is used for donating more substantial quantities of blood that require a faster blood flow rate, such as blood donor units and therapeutic phlebotomy. The 18g needle comes attached to the collection bag and does not require additional assembly.
21 Gauge Needles
21g needles are the most common gauge of needles used for routine blood draws and venipuncture. The gauge is small enough in which it does not cause any significant pain or discomfort during use. For most patients, their veins are of a size and stability that is best suited for the 21g needle. In some circumstances, however, it may be required to use a smaller size needle than 21g.
The 21g needle does not force blood through a narrow needle bore, which prevents the rupture of the blood components that need to be analyzed and ensures specimen integrity. The 21g needle allows blood to flow at a steady rate, which accelerates collection time and is traditionally color-coded with a green covering.
22 Gauge Needles
Depending on the facility, 22g needles are occasionally utilized for routine blood draws. The slightly smaller size may assist the phlebotomist with slightly smaller veins they may encounter on older children or adult patients. This needle can be assembled with the more common multi-sample needle ETS system and tends to have a black color code covering.
23 Gauge Needles
23g needles, also known as butterflies, are used when a person’s vein is much narrower than average. It is light blue color coded. Despite the phlebotomist’s efforts to anchor the vein, the patient may be unwell or have minimal sites to choose a vein from, requiring a smaller needle.
Small children and infants are the most common patients to be drawn on using a 23g needle also as their veins are naturally much thinner than those of an adult. Some adult veins, however, do require the use of a butterfly.
23g needles are part of a winged infusion system (butterfly), not the multi-sample needle ETS system. Needles smaller than a 23g might hemolyze the red blood cells, and the sample could not be processed for testing. For instance, a 25g needle is better suited for intramuscular injections than blood draws.
Gaining Experience with Various Needle Gauges
In our Certified Phlebotomy Technician I (CPT I) course, PhlebotomyU students earn practical experience with multiple needle types. Through this course, our students gain over 80 hours of in-classroom knowledge and 40-120 hours at an externship site to enhance their phlebotomy skills.
To learn more about needle gauges and our CPT I course, contact PhlebotomyU today.