📘 Insulin injection technique

You can inject insulin in the abdomen (fastest absorption, avoid 5 cm around the navel), thighs (slower absorption, good for basal insulin), arms (upper outer area, to be avoided) and buttocks (slow absorption, sometimes useful in children). The abdomen is ideal for rapid insulin due to faster and more predictable absorption, while thighs are good for long-acting insulin.

Each area has multiple injection sites. Mentally divide the area into squares with three cm sides and use a different site for each injection. Do not use areas with lipodystrophy (lumps or indentations), bruises, scars or signs of inflammation. Keep the same area for the same type of insulin (for example, rapid in the belly, long-acting in the thighs) for more predictable absorption.

Systematic rotation prevents lipodystrophy and ensures consistent absorption. Divide the abdomen into four quadrants and use one quadrant per week, or move in a circle around the navel (don't get too close to it!) like a clock. Leave at least two cm between two consecutive injections and do not reuse the exact same site for at least one month.

You can make a mental map of the sites used. Some people use the left/right sides of the abdomen alternately. For example, Monday, Wednesday and Friday on the left, Tuesday, Thursday and Saturday on the right. For evening basal insulin, keep one side for a month and then switch to the other side. Adjust the dose if you notice left/right differences. Visually check and regularly palpate injection areas to detect lumps or areas of local fat deposition early.

Insulin should be injected into subcutaneous tissue (the fat under the skin), not into muscle or superficially into the skin. With 4 mm needles, inject perpendicular (90 degrees) without making a skin fold. With standard 6-8 mm needles, make a skin fold and inject at 45 degrees. Needles longer than 8 mm increase the risk of intramuscular injection and should only be used by people with excess subcutaneous fat.

Most adults can use 6 mm needles without problems. If you are very thin or have very little subcutaneous tissue, you can try 4 mm needles (from children). Accidentally injecting intramuscularly is painful, may bleed slightly, and insulin absorption is up to 50% faster (less pronounced with ultra-rapid analogs). In conclusion, if you hit the muscle you will feel greater resistance and pain.

Disinfecting the skin with alcohol before insulin injection is not necessary. If the skin is clean, modern recommendations no longer require this for routine situations. Alcohol can dry and irritate the skin with repeated use and does not significantly reduce the (very small) risk of infection. Wash your hands before preparing insulin and make sure the injection area is visibly clean.

If you prefer to disinfect or the doctor recommends it (weakened immune system, poor hygiene conditions), use 70% alcohol and let it evaporate completely before injection. Wet alcohol can cause a burning sensation when the needle passes through the skin. At home, with single-use needles (unfortunately less commonly used that way) and normal hygiene, the risk of infection is extremely small.

The official recommendation is to use a new needle for each injection. Needles become slightly dull even after the first use (visible under microscope), which makes subsequent injections increasingly painful and can traumatize subcutaneous tissue. Reused needles (especially detached ones) may have crystallized insulin residue and can carry bacteria.

In reality, many people reuse needles a few times for economic or convenience reasons. Avoid reusing a needle for more than one day. Never share needles with anyone else, even after disinfection. If you reuse, put the cap back on immediately after use and don't touch the needle with anything. At the first sign of increased pain or resistance to injection, change the needle.

Bruises occur when the needle hits and breaks a small capillary vessel. This is normal to happen occasionally and does not affect insulin absorption. Such small bruises may occur somewhat more frequently if you take aspirin (in low dose) or anticoagulants, have vitamin K deficiency or increased capillary fragility. Injecting too quickly or using the same needle multiple times increases the risk of bruises.

To minimize bruises, inject slowly and steadily, do not massage the area immediately after injection, and use new needles. If blood appears on the skin after insulin administration, apply light pressure (not massage) with a clean cotton pad. Bruises disappear on their own in ten days and do not require treatment. Avoid the bruised area for subsequent injections until it heals completely.

Use new and short needles (4 mm), let the insulin reach room temperature (take it out of the refrigerator 15-30 minutes before), inject slowly and steadily, and relax the muscles in the injection area. Avoid areas with many nerve endings, such as the edge of the abdomen, too close to the navel, knees or other joints. Distract yourself and breathe deeply.

If you use insulin from a new refrigerated vial or pen, "cold burn" pain is common. Keep the insulin you are currently using at room temperature for up to three weeks. Some people apply an ice cube for ten seconds before injection to locally numb the area (logistically difficult). Do not use anesthetic creams as they can affect absorption.

Although not medically recommended, the reality is that many people reuse needles a few times. The assumed risks include increased pain (the needle becomes visibly dull), lipodystrophy (repeated tissue trauma), local infections (rare but possible), incorrect dosing (insulin crystals can block the needle) and cartridge contamination (bacteria can enter through the needle).

If you decide to reuse for economic reasons, limit to maximum 3-4 uses, never more than 24 hours, keep the cap on between uses, don't touch the needle and change immediately if you bend the needle or feel increased resistance. Never reuse if you have active infections, weakened immune system or healing problems. Calculate if the savings are worth the risks. In general, needles are relatively inexpensive.

A little blood after injection is not a problem. It means you hit a small capillary and is not dangerous at all. Apply light pressure with a cotton pad or clean tissue for 10-30 seconds. Do not massage the area. This can spread insulin in the tissue and accelerate absorption in an unpredictable way.

If bleeding continues for more than a minute or a large bruise appears, apply firmer pressure and possibly ice. Note in your journal if blood glucose behaves differently after an injection that bled. This is very rare. Faster absorption may occur only if you hit a larger vessel. Frequent bleeding may indicate needles that are too long, hitting muscle, or clotting problems that may require additional investigation (very unlikely).

Unused insulin is stored in the refrigerator at 2-8°C, ideally in the middle section (not in the freezer or on the door where temperature varies). The vial or pen in use is kept at room temperature (below 25°C) for maximum three weeks. Some insulins can last longer, but you should also allow for a safety margin. Do not expose insulin to direct light, extreme heat or freezing.

For transport, use an insulated case, do not leave insulin in the car, especially in summer or winter. At the airport, carry insulin in hand luggage, accompanied by a medical letter. Insulin should not be shaken violently (it foams and affects dosing). Insulin analogs (long-acting or rapid) no longer need shaking (mixing) before use, as in the case of NPH insulin. Always check the appearance before use. Do not use it if it's cloudy (except NPH), has crystals or changed color.

Technically you can inject through thin clothes (shirt, thin t-shirt), but it is not recommended at all. Textile fibers can contaminate the needle, you can't see exactly where you're injecting and you may incorrectly rotate injection areas. Thick clothes deflect the needle and affect injection depth.

If you have an emergency and no alternative, make sure the clothing area is clean, use a new needle, inject through only one thin layer of clothing and be very careful about injection depth. Only do this exceptionally. Most people find a discreet way to lift their clothing slightly for direct access to the skin.

Lumps (lipohypertrophy) occur from repeated injection in the same area. Fatty tissue proliferates abnormally in response to insulin's trophic effect. They are soft, painless, but absorb insulin unpredictably, sometimes with delay, sometimes not at all. They occur in a quarter of people who do not correctly rotate injection sites and are more common in those who reuse needles.

For prevention, systematically rotate injection sites, use new needles, regularly check and palpate injection areas. If you already have lumps, completely avoid that area for at least three months. Never inject into lumps. Glycemic control will be chaotic. Show the doctor all areas with changes to evaluate your injection technique together.