🩺 Subcutaneous Injection

Subcutaneous (SC) injection delivers medication into the layer of fat between the skin and the muscle. It is designed for drugs that require slow, steady absorption, such as insulin and heparin. The technique requires careful site selection (typically the abdomen, thighs, or upper arms) and rotation to prevent tissue damage. Maintaining an aseptic non-touch technique (ANTT) and ensuring the correct depth of injection are critical to patient safety and drug efficacy. It is a fundamental skill for managing chronic conditions and providing end-of-life care in UK clinical practice.

The subcutaneous (SC) route is used for medications intended for slow, sustained absorption into the systemic circulation via the capillaries in the adipose tissue. It is the primary route for insulin administration in diabetic patients. It is also used for anticoagulants like Low Molecular Weight Heparin (LMWH) and certain biologics or hormones (e.g., GNRH analogues). In palliative care, the SC route is frequently used for continuous symptom control via a syringe driver or for 'PRN' breakthrough medications when the oral route is no longer viable. Some vaccines are also administered via this route.

Subcutaneous injections should not be performed on skin that is inflamed, oedematous, or shows signs of infection or ulceration. Sites with significant lipohypertrophy, scarring, or moles should be avoided to ensure consistent drug absorption. This route is generally avoided in patients with peripheral circulatory collapse or shock, as reduced blood flow to the skin leads to poor and unreliable absorption. While anticoagulation is not an absolute contraindication, particular care is needed to avoid large haematomas. It is contraindicated if the patient has a known allergy to any component of the medication.

Prescription chart and patient identity. Clean procedure tray and non-sterile gloves. The medication (e.g., insulin pen, pre-filled syringe of LMWH, or vial). 25G to 27G short, fine-gauge needle. 1ml or 2ml syringe (if not using pre-filled). Alcohol swab (if indicated by local policy, though often not required for insulin). Gauze and adhesive plaster. Sharps disposal container and clinical waste bag. Identification of suitable landmarks on the abdomen, thighs, or upper arms.

Verify the patient's identity and explain the procedure, ensuring consent is obtained. Wash hands and prepare the medication using ANTT. Select a site with sufficient adipose tissue, such as the abdomen or outer thigh. Clean the area if necessary and allow it to dry. With the non-dominant hand, gently pinch a fold of skin to elevate the subcutaneous tissue from the underlying muscle. Insert the needle quickly at a 90-degree angle (or 45-degree if the patient is very thin). Inject the medication slowly. If using a pen, wait 5–10 seconds before withdrawing. Release the skin and withdraw the needle. Apply light pressure with gauze but do not massage. Dispose of the needle immediately in the sharps bin and document administration.

Interpretation involves assessing the patient's response to the medication and monitoring for local complications. For insulin, this means monitoring blood glucose levels to ensure efficacy. The injection site should be inspected regularly for signs of lipohypertrophy (rubbery lumps), bruising, or inflammation. Clinicians must interpret the patient's ability to self-inject, assessing their manual dexterity and understanding of site rotation. A successful procedure is indicated by the delivery of the full dose with minimal discomfort and the absence of complications like bleeding or infection at the site.

Common errors include failing to rotate the injection site, which leads to lipohypertrophy and subsequent unpredictable absorption. Many students or patients forget to pinch a skin fold in thin individuals, risking an accidental intramuscular injection. Injecting too quickly or into 'bruised' skin can cause pain and haematoma. Another frequent mistake is massaging the site after injection, which can speed up absorption too much or cause tissue trauma. Not holding the needle in place for the required few seconds (especially with insulin pens) can lead to 'wet' injections where medication leaks out.

Always check the prescription and patient ID carefully. For OSCEs, state clearly that you are checking the expiry date and the appearance of the medication. When using the abdomen, remind the examiner you will stay at least 2 inches away from the umbilicus. Pinch a fold of skin (if appropriate for the patient's habitus) and insert the needle at a 45-degree or 90-degree angle depending on needle length and fat thickness. Do not rub the site afterwards. Ensure the sharps bin is brought to the 'point of care' to avoid walking across the room with an unsheathed needle.

The UK MLA requires students to be proficient in the 'Six Rights' of medicine administration and the safe use of sharps. Understanding the pharmacokinetic benefit of SC administration (slow release) vs IM (rapid release) is essential medical knowledge. Students should be aware of the common sites for SC injection, specifically the abdomen (avoiding the umbilicus). The management of needle-stick injuries and the importance of sharps safety are key aspects of clinical governance tested in the MLA. Awareness of patient education regarding site rotation is a core communication skill.