A subcutaneous (SC) injection delivers medication into the layer of fatty tissue (subcutis) just beneath the skin. This route is chosen for medications requiring a slower, sustained absorption rate into the bloodstream. Since the adipose tissue has fewer blood vessels than muscle, the drug is absorbed gradually. Common medications administered this way include insulin, certain blood thinners, and some fertility drugs. The arm is a common site for this procedure due to its accessible and sufficiently fatty location.
Essential Preparation and Supplies
Preparation begins with meticulous hand hygiene, washing thoroughly with soap and water for at least 20 seconds. Gather all necessary supplies on a clean, dry work surface, including the medication, a sterile syringe and needle, alcohol swabs, and an approved sharps container. Inspect the medication for clarity, ensuring there are no floating particles, and confirm the expiration date is valid. If the medication is refrigerated, remove it about 30 minutes before the injection to allow it to warm to room temperature, which reduces discomfort.
If using a single-dose vial, clean the rubber stopper with an alcohol swab and allow it to air dry. To prevent a vacuum, draw an equivalent amount of air to the prescribed dose into the syringe. Inject this air into the vial, then invert the vial, ensuring the needle tip remains submerged in the fluid. Pull back the plunger to draw the correct dose of medication, and gently tap out any visible air bubbles before the injection. Pre-filled pens or auto-injectors may require priming by ejecting a small test dose to ensure the device is working correctly.
Selecting and Preparing the Arm Injection Site
The appropriate injection site is the fleshy outer or back area of the upper arm, which provides a reliable layer of subcutaneous fat. Locate this area approximately one hand width down from the shoulder and one hand width up from the elbow. Avoid the shoulder joint, the elbow, or any areas near major nerves or blood vessels. Inspect the chosen site for irritation, bruising, hardness, or scarring, as these conditions interfere with proper medication absorption.
For repeated injections, site rotation is necessary to prevent tissue damage, such as hardened lumps or fat atrophy. Place a new injection at least one inch away from the previous site to allow tissue recovery and ensure consistent medication effectiveness. Cleanse the selected location with an alcohol swab using a firm, circular motion, starting at the center and moving outward. Allow the skin to dry completely before the injection to prevent stinging.
Step-by-Step Subcutaneous Injection Technique
Gently grasp and pinch a fold of skin and fatty tissue between the thumb and index finger to lift the subcutaneous layer away from the underlying muscle. The size of the fold determines the insertion angle: a two-inch pinch allows for a 90-degree insertion. A one-inch pinch or less requires a 45-degree angle, especially for thinner individuals, to prevent the needle from reaching the muscle. Hold the syringe like a dart and insert the needle with a quick, single, smooth motion into the pinched skin to minimize pain.
Once the needle is fully inserted, release the pinched skin to avoid injecting the medication under pressure. Administer the medication by slowly and steadily depressing the plunger until the syringe is completely empty. Injecting the fluid too rapidly increases discomfort and may cause tissue damage. Wait for up to ten seconds before withdrawal, allowing the medication to disperse into the tissue and preventing leakage.
Withdraw the needle smoothly at the exact same angle at which it was inserted to prevent tearing the tissue. Aspiration (pulling back on the plunger to check for blood) is an older technique no longer recommended for most modern subcutaneous injections. This practice is unnecessary because the subcutaneous layer has few large blood vessels, and the risk of hitting a vessel is low. Attempting to aspirate can increase pain and destabilize the needle.
Post-Injection Care and Safe Disposal
After the needle is withdrawn, apply a clean piece of gauze or a cotton ball to the injection site with light, gentle pressure. If minor bleeding occurs, holding pressure for a few seconds is typically sufficient to stop it. Do not rub the injection site, as this can force the medication into the muscle or cause local tissue irritation. Minor bruising, a small red spot, or mild soreness is a common reaction that usually resolves within a few days.
Immediately dispose of the used syringe and needle into an approved, puncture-resistant sharps container. Never recap needles after use, as this is the most common cause of accidental needlestick injuries. Drop the entire needle and syringe assembly into the container without delay. Never place used sharps in regular trash or recycling bins, as this poses a serious risk to others.
Keep the sharps container out of the reach of children and pets, and only fill it up to the indicated line (typically three-quarters full). Once full, securely seal and tape the lid shut to prevent accidental opening. Disposal of the full container varies by location. Always follow specific local guidelines or manufacturer instructions for final disposal, which may include:
- Drop-off programs at hospitals or pharmacies.
- Mail-back programs.
- Sealing and labeling the container before placing it in household trash (in some jurisdictions).