Definition: An intradermal injection (ID) puts a small amount of liquid into the skin itself, in its top layers. It is shallower than a subcutaneous shot, which goes into the fat below the skin. The best-known example is the tuberculin skin test, also called the Mantoux test.
Tubersol is a tuberculin test labeled for intradermal injection only. Its label gives a test dose of 0.1 mL, with the inner forearm as the preferred site. The needle point goes into the most superficial layers of the skin with the bevel facing up, and the liquid is pushed in slowly.
The label says a properly given intradermal injection raises a pale bump (a bleb) about 10 mm across, which fades within minutes. The test is read by a trained health professional 48 to 72 hours later, and only the firm swelling counts, not the redness.
Depth is the whole difference. Intradermal is in the skin, SubQ is in the fat under it, and intramuscular (IM) is deeper still, in muscle.
CDC guidance on vaccines says most injectable vaccines are given IM or SubQ, and that giving a vaccine by a route other than the recommended one might reduce how well it works or raise the risk of local reactions. CDC also notes that hepatitis B vaccine given intradermally may produce a weaker antibody response than the same vaccine given into the deltoid muscle.
The route belongs to the product. A label that says subcutaneous does not cover an intradermal shot, and the reverse is also true. GLP-1 pens like Ozempic and Mounjaro are labeled for subcutaneous use. When you log a dose, record the route along with the site so that anything unusual, like a shot that went in shallower than planned, is on record.
Read more on Dose Track: How to log a dose · Logging injection sites