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Venipuncture 101: What to Know About Gauge Needles

Venipuncture 101: What to Know About Gauge Needles

In contrast to conventional measurement systems, the relationship between gauge and needle size is inverse. The needle width narrows as the gauge increases. For example, 22g is slimmer than 21g, despite the “larger” number. There is no standard gauge size for phlebotomy patients. Each needle has a different blood flow and vein compatibility.

Read on to learn more about gauge needles and understand the different types and their respective function.

Understanding Venipuncture and Gauge Needles as Tools

A chemist, bacteriologist, parasitologist, lab worker, nurse, paramedic, or student uses venipuncture to draw blood from a vein. It is sometimes referred to as phlebotomy.

Although needles of 21, 22, and 23 gauge are known to be commonly used, a phlebotomist should be conversant with all needle types in order to manage vein and tissue diameters of varying sizes. This allows for a seamless venipuncture on different patients.

Depending on the test, 5 to 25 mL are typically removed. Blood is deposited in a commercially manufactured test tube for transit and storage according to laboratory regulations.

Diabetic patients, neonates, and blood donors can all provide blood samples. Polycythemia patients get 350-500 cc of blood collected via venipuncture. Blood or blood component tests can help a doctor diagnose and/or treat a patient.

Gauge Needle Size 18

18g needles are not used for blood draws. This needle size is used in blood donor units and therapeutic phlebotomy, where a faster blood flow rate is required. The 18g needle is already assembled on the collection bag.

Gauge Needle Size 21 (Green)

21g needles are often used for blood draws and venipunctures. This specific gauge size is meant to lower discomfort or agony during use. The majority of veins are large and strong enough to accommodate a 21g needle, however, a needle smaller than 21g is occasionally required.

The 21g needle does not compress blood into a tiny needle bore, preserving the specimen's integrity. The 21g needle ensures consistent blood flow, which speeds up blood collection. It is also colour-coded green.

Gauge Needle Size 22

For routine blood draws, 22g needles are sometimes used. This is best used for veins in older children or adults. A multiple-sample ETS approach can be used to create this black-coated needle.

Gauge Needle Size 23 (Blue)

23g winged or butterfly needles, which are colour-coded blue, are used for thin veins. Despite the phlebotomist's efforts, the patient may be ill or have limited venous access, necessitating the insertion of a smaller needle.

Because newborns and young children have smaller veins, a 23g needle is commonly used to draw blood. Certain adult veins necessitate the use of this gauge needle size in some cases.

The 23g needles are from a butterfly (or winged) infusion system, not an ETS system. Red blood cells can be hemolysed by needles smaller than 23g, making testing impossible.


Understanding the purpose of venipuncture and the different types of needles is not only beneficial for practitioners everywhere. Such knowledge could also be helpful and useful among patients or loved ones of patients.

Now that you are more aware of the needles used for blood extraction and blood tests, there will be a better relationship between doctors or nurses and patients. After all, it’s just as crucial to learn about the process of each health condition as opposed to simply seeking treatment.

Are you looking to buy needles online? UKMEDI offers a full range of medical needles and syringes for your medical supplies. Browse our online shop today!

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