Introduction
Intramuscular (IM) and subcutaneous (SC) injections are clinical skills assessed in virtually every UK medical school OSCE and among the most commonly performed practical procedures in hospital and community settings. Safe, aseptic technique — including correct site selection, angle, needle size, and post-procedure care — reduces complications including infection, nerve injury, inadvertent IV administration, and lipodystrophy.
Key Differences: IM vs SC Injection
| Feature | Intramuscular (IM) | Subcutaneous (SC) |
|---|---|---|
| Angle of insertion | 90° | 45° (or 90° for insulin pens with short needles) |
| Needle gauge | 21–23 G | 25–27 G |
| Needle length | 25–38 mm | 16 mm |
| Volume | Up to 5 mL (deltoid: up to 2 mL) | Up to 1.5 mL |
| Absorption speed | Faster (muscle vascularity) | Slower, more sustained |
| Common uses | Vaccines, haloperidol, methotrexate, antibiotics | Insulin, heparin, enoxaparin, growth hormone |
Equipment Required
Gather all equipment before approaching the patient (ANTT principle):
- Appropriate needle and syringe (check gauge and length for route)
- Medication (check 5 Rights: right patient, drug, dose, route, time)
- Alcohol-based skin prep swab (70% isopropyl alcohol)
- Cotton wool or gauze
- Sharps bin (within arm's reach before starting)
- Non-sterile gloves
- Drug prescription chart
🧠 Mnemonic
DARTS — IM/SC Injection Framework
D — Draw up medication correctly; check drug chart and 5 Rights
A — Aseptic Non-Touch Technique (ANTT) throughout
R — Right site for route (deltoid, ventrogluteal, vastus lateralis for IM; abdomen, thigh for SC)
T — Technique: 90° Z-track for IM; 45° pinch-up for SC
S — Sharps: never resheath; dispose directly into sharps bin immediately after withdrawal
Consent and the 5 Rights
Before any injection:
- 1Confirm patient identity (name, DOB, hospital number — check against wristband)
- 2Check drug prescription: right patient, right drug, right dose, right route, right time
- 3Check for allergies
- 4Obtain verbal consent and explain the procedure
- 5Ask about previous reactions to injections or known clotting disorders
ANTT — Aseptic Non-Touch Technique
ANTT is the UK standard framework for infection prevention in clinical procedures:
- Key parts (needle tip, syringe tip, bung, vial top) must NEVER be touched or contaminated
- Key site (the injection site) must be appropriately cleaned
- Use non-sterile gloves, alcohol swab preparation, and avoid touching key parts at all times
Intramuscular Injection Site Selection
| IM Site | Location | Volume | Advantages | Risks |
|---|---|---|---|---|
| Deltoid | 3 finger widths below acromion, lateral upper arm | Up to 2 mL | Easily accessible, quick absorption | Radial nerve if too low; brachial artery if too medial |
| Ventrogluteal (VGL) | Triangle formed by iliac crest, ASIS, and greater trochanter | Up to 5 mL | No major nerves or vessels; preferred in adults | Requires correct positioning |
| Vastus lateralis | Middle third of anterolateral thigh | Up to 5 mL | No major nerves; good in infants and children | Less commonly used in adults |
| Dorsogluteal | Upper outer quadrant of buttock | Up to 5 mL | Large muscle | Risk of sciatic nerve injury — not recommended as first choice |
⚠️ Red Flag
The dorsogluteal site carries a risk of sciatic nerve injury if not precisely located. It is no longer recommended as the first-choice IM site in UK practice — use the ventrogluteal or deltoid in preference. In your OSCE, if asked to identify the safest IM site, choose the ventrogluteal.
Intramuscular Injection Technique
- 1Wash hands and don non-sterile gloves
- 2Draw up medication aseptically: clean vial bung with alcohol swab, allow to dry, draw up with a drawing-up needle, then change to the injection needle
- 3Expel air bubbles by tapping the syringe and gently pushing the plunger until a small drop appears at the tip
- 4Expose and identify the injection site; clean with alcohol swab using a circular outward motion; allow 30 seconds to dry — wet alcohol is painful and its antibacterial properties require drying
- 5Use your non-dominant hand to spread the skin taut over the site
- 6Insert the needle at 90° with a smooth, swift motion — do not hesitate
- 7Apply the Z-track technique (see below)
- 8Inject medication slowly (approximately 1 mL per 10 seconds for larger volumes)
- 9Withdraw at the same angle; immediately apply gentle pressure with cotton wool — do not rub
- 10Immediately place the needle in the sharps bin — never resheath
Z-Track Technique
The Z-track technique prevents medication tracking back along the needle path into subcutaneous tissue, minimising pain, irritation, and staining (e.g. iron injections):
- 1After cleaning the site, use your non-dominant hand to pull the skin and subcutaneous tissue approximately 2–3 cm laterally
- 2Hold this displacement throughout the injection
- 3Insert the needle at 90° and inject slowly
- 4Wait 10 seconds after injection before withdrawing
- 5Withdraw the needle and release the skin simultaneously
- 6The needle track is now displaced — this seals the medication in the muscle
💎 Clinical Pearl
The Z-track technique is mandatory for iron dextran injections to prevent painful skin staining, but it is good practice for all IM injections and demonstrates technique sophistication in the OSCE.
Subcutaneous Injection Technique
SC Injection Sites
- Abdomen: 2.5 cm either side of the navel; most commonly used for insulin and heparin
- Upper outer thigh: insulin, vaccines, enoxaparin
- Rotate sites systematically to prevent lipodystrophy (insulin) or bruising (heparin)
SC Injection Steps
- 1Clean the site with an alcohol swab; allow to dry
- 2Using thumb and forefinger, pinch up a fold of subcutaneous tissue
- 3Insert the needle at 45° (or 90° for insulin pens with very short needles ≤6 mm)
- 4Inject steadily; hold in place for 10 seconds before withdrawing
- 5Withdraw at the same angle; apply gentle pressure — do not massage (massage disperses insulin unpredictably)
- 6Dispose of needle immediately into sharps bin
Sharps Safety
- Never resheath a needle with two hands — if necessary, use the one-hand scoop technique
- Sharps bins must be no more than three-quarters full before disposal
- Label sharps bins with ward, date, and signature
- Report needlestick injuries immediately: wash with soap and water, do not squeeze, report to occupational health, and start post-exposure prophylaxis (PEP) if indicated
⚠️ Red Flag
A needlestick injury requires immediate action: wash the site thoroughly with soap and water, report to your supervisor, attend occupational health or A&E out of hours, and start HIV PEP within 1 hour if the source patient has known or suspected HIV. Document the incident in full.
FAQs
"What gauge and length needle should I use for IM injection into the deltoid?"
For a standard adult deltoid IM injection, use a 23 G, 25 mm needle. In an obese patient, a longer needle (38 mm) may be required to ensure the medication reaches muscle. In a very thin or cachectic patient, a shorter needle may suffice. Document your rationale for needle selection.
"Why should I allow the alcohol swab to dry before injecting?"
Wet alcohol introduced into tissue is painful, may inactivate some live vaccine preparations, and does not exert its full antibacterial effect. Allow at least 30 seconds for drying. This is a commonly missed mark in practical OSCE stations.
"How do I prevent lipodystrophy at SC injection sites?"
Systematic rotation of injection sites prevents lipodystrophy (hypertrophy or atrophy of subcutaneous fat) in patients on regular insulin or other SC medications. Lipodystrophic tissue has erratic insulin absorption — injecting into it causes unpredictable glucose control.
"Can I give an IM injection through clothing?"
No — always expose the site to confirm the correct location, assess skin integrity, clean appropriately, and avoid injecting into a lipoma, inflamed skin, haematoma, infected area, or oedematous tissue.
"Should I aspirate before an IM injection?"
Current WHO guidance (2016) does not recommend routine aspiration before IM injection. The risk of intravascular injection at recommended sites (deltoid, ventrogluteal, vastus lateralis) is negligible with correct technique. Follow local trust protocol and in the OSCE, state current guidance clearly.
Related Posts
- Venepuncture & Cannulation OSCE — ANTT, peripheral cannulation, and safe blood-taking technique
- Prescribing Safety OSCE — drug chart completion, dose checking, and route verification
- Drug History OSCE — medication reconciliation and identifying injection-related drugs in a drug history