Diabetes needle sizes and how to choose the right one for you

Diabetes needle sizes : The insulin is administered in the subcutaneous tissue , located between the skin and muscle, where it is deposited and where it absorbs slowly (will find more information in the article Injecting insulin ).

You should avoid injecting insulin inside the skin (intradermal injection), as it is very painful. Injecting it into the muscle should also be avoided , because it changes the speed of insulin absorption, which increases the glycemic variability and leads to more hypoglycaemia and unexplained hypoglycaemia.

To ensure an adequate insulin puncture, several factors must be taken into account:

  1. Choose the appropriate puncture zones and establish a good pattern of rotation of zones .
  2. Avoid injecting in areas with lipodystrophy and scars.
  3. Take a skinfold or pinch with the index finger and thumb in an appropriate manner .
  4. Count 10 seconds after injecting the insulin, in order to wait a reasonable time before removing the needle and avoid the reflux of insulin.
  5. Choose a needle of adequate length.
  6. Avoid the reuse of needles.

How to choose a needle of adequate length

In recent years there have been many improvements, both in the length and in the thickness of the needles, which have led to the modification of the criteria to choose the right needle. Currently, the following aspects must be taken into account:

  1. Less thickness, less pain: the needles are bevelled at the tip to minimize damage at the time of puncture, but the thickness of the needle also influences. The thickness of the needle is measured in gauges and is expressed with a G. The greater the number of G, the smaller the thickness. The least painful needles are those that are 31G and 32G thick.
  2. Adapting the insulin needle to the thickness of the skin : according to several studies carried out to analyze the thickness of the skin in children as well as in healthy adults, with diabetes, with obesity and of different ethnic groups, most people have a thickness of skin between 2.0 and 2.5 mm, although it can vary between 1.25 and 3.25 mm. The skin of children is slightly less thick than adults, especially between 2 and 6 years old. The subcutaneous fat of children increases in thickness at puberty, until it reaches adult levels. In very thin and young people, intramuscular injections occur more frequently if long needles are used. Therefore, the shortest needles that exist in the current market, 4 mm in length, reliably cross the skin of all people, both children and adults, so that insulin reaches the subcutaneous fat without problems .
  3. Shorter needles are much safer, better tolerated and less painful : it is known that the 8 mm long needle (which was recommended a few years ago) increases the risk of intramuscular puncture.
  4. The right needles should measure a maximum of 6 mm in length : those with lengths of 8 mm or more are not recommended in all people who need to take insulin.
  5. The shortest length for pen or ballpoint pen is 4 mm and the syringe length is 6 mm, as it must pass through the cap of the insulin vial.

How to pierce the insulin according to the length of the needle

If you carry a pen or pen:

4 mm needle It must be inserted perpendicular to the skin.

In children of 6 years or less and very thin people it is preferable to take a skin fold and insert the needle at a perpendicular angle.

5 mm needle Always take skin fold and insert the needle at a perpendicular angle.
6 mm needle It is preferable to use shorter needles.

If it is the only option we have, we should take a skin fold and insert the needle at an angle of about 45º.

If you have an insulin pump :

There are different types of cannula for insulin pump , depending on the material they are composed of and the insertion angle:

  1. According to the material, there are cannulas of two types:
    • Stainless steel , with which the needle is inserted fixed. In our environment, these cannulas are used mainly by those few people who have Teflon allergies.
    • Teflon , much more flexible.
  2. Depending on the type of insertion, there are cannulae:
    • Of perpendicular insertion , that are punctured forming a right angle with respect to the body.
    • Of oblique insertion , that are punctured with a more or less inclined angle depending on the amount of fatty tissue that each person has. Some pump brands have an inserter to make the cannula tilted.

Usually, the perpendicular cannula and, in our environment, Teflon are chosen. Its insert leaves less mark on the skin, is simpler and less “traumatic” for children.

The proper length of the cannula depends on the thickness of the subcutaneous fat of the person with diabetes. The perpendicular insertion cannulae are shorter than the oblique insertion cannulas.

Perpendicular insertion cannulas Oblique insertion cannulas
6 mm 13 mm
8 mm 17 mm
9 mm

The cannulas that present less risk of intramuscular injection are those of 6 mm in length. Very thin children may need to take a skin fold to minimize the risk of intramuscular insertion.

In people with a great thickness of subcutaneous fat the cannula of 8 or 9 mm in length can be used, depending on the model of insulin pump that they carry. Very thin, muscular or very active people whose thickness of the subcutaneous fat is very thin, should consider the use of cannulas of oblique insertion of 30-45º.

If the bent tip is observed when removing the cannula or there are many non-infusion alarms in the pump, consider switching to a shorter cannula or oblique cannula.

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