Which statement best distinguishes a subcutaneous injection from an intramuscular injection in terms of needle angle and target tissue?
- ASubcutaneous injections enter adipose tissue at 45 or 90 degrees depending on body build, while intramuscular injections enter muscle at 90 degrees. Correct
- BSubcutaneous injections enter muscle at 45 degrees, while intramuscular injections enter the dermis at 90 degrees.
- CSubcutaneous injections enter the dermis at 5 to 15 degrees, while intramuscular injections enter adipose tissue at 45 degrees.
- DSubcutaneous injections enter muscle at 90 degrees, while intramuscular injections enter adipose tissue at 45 degrees.
Why A is correct: Correct. Subcutaneous medication is deposited into the adipose layer beneath the dermis, where slower absorption is desired, and the angle is adjusted to body habitus. Intramuscular medication is deposited into well-vascularised muscle, which requires a perpendicular 90 degree approach to traverse skin and subcutaneous tissue and reach the muscle belly.
Why B is wrong: Tempting because both terms are listed and 45 and 90 degrees are correct injection angles in other contexts, but the target tissues are reversed. Subcutaneous targets fat under the dermis, not muscle, and intramuscular targets muscle, not the dermis.
Why C is wrong: This conflates subcutaneous with intradermal technique. 5 to 15 degrees and a dermal target describe intradermal injections used for tuberculin and allergy testing, not subcutaneous, and IM injections do not stop in adipose tissue.
Why D is wrong: This swaps the two routes entirely. The deeper target (muscle) requires the steeper perpendicular angle, and the shallower target (subcutaneous fat) uses the lesser angle, so the assignments here are inverted.