Subcutaneous injection

What it is

The subcutaneous (SC) route delivers a small volume of drug into the fatty tissue between skin and muscle, where it is absorbed gradually. It is used for insulins, low-molecular-weight heparins and some vaccines. Common sites are the abdomen (away from the navel), the outer upper arm and the front of the thigh. A skin fold is pinched, the needle goes in at 45° or 90° depending on the fat layer, and the site is not massaged.

Indications

• Insulin and anticoagulants ordered subcutaneously.
• Some vaccines given by this route.
• Drugs given in a small volume.

Contraindications and precautions

• Do not inject into bruised, open or scarred skin, or where blood flow is poor (for example cellulitis).
• Avoid the area around the navel and bony prominences.
• Anticoagulants: check for active bleeding or abnormal clotting tests per protocol.
• Insulin: know the blood glucose and the meal plan before giving it.

Equipment

• Prepared medication and medical order.
• An insulin syringe marked in units (for insulin only) or a small syringe; a short, fine needle (25 to 31 gauge).
• Alcohol swab and sterile gauze.
• Clean gloves.
• Sharps container.

Step by step (and why)

1. Apply the rights and the double check if it is insulin or an anticoagulant — these are high-alert drugs.
2. Choose a site different from the last dose, within the same region for insulin — rotation prevents skin hypertrophy and bruising.
3. Clean the skin and let the alcohol dry — reduces infection and stinging.
4. Pinch a skin fold with the non-dominant hand — lifts fat away from muscle.
5. Insert the needle at 45° or 90° depending on the fat layer — leaves the drug in subcutaneous tissue.
6. Release the fold once the needle is in; with heparin or an insulin pen, hold it until just before withdrawing — the technique for each product.
7. Inject slowly and withdraw at the same angle — reduces pain.
8. Press gently with gauze without massaging — massage can cause a haematoma.
9. Discard the needle in the sharps container and document the site — allows rotation at the next dose.

Complications

• Bruising, especially with anticoagulants or if the site is massaged.
• Skin hypertrophy at insulin sites that are not rotated.
• Hypoglycaemia if insulin does not match meals or the wrong insulin is given.
• Bleeding with anticoagulants.

Next step: when to call for help

• Sweating, tremor, confusion or low blood glucose after insulin: follow the hypoglycaemia protocol and report at once.
• Bleeding gums, dark or red urine, or black stools on anticoagulants: tell the doctor.
• A large or growing bruise at the site: report.
• Doubt about the insulin type or dose: do not give it until clarified with the prescriber.

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Educational content for students; it does not replace your institution's protocols, supervised clinical training or a prescriber's order. Dose-calculation examples use made-up numbers: they are educational, not a clinical order.

Sources: Nursing Skills (Open RN), 18.5 Administering Subcutaneous Medications (Open RN, Chippewa Valley Technical College (LibreTexts), 2022); Nursing Skills (Open RN), 18.8 Checklists for Parenteral Medication Administration (Open RN, Chippewa Valley Technical College (LibreTexts), 2022); Vaccine Administration (General Best Practice Guidelines for Immunization) (Centers for Disease Control and Prevention (CDC), 2024).

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