What is an Intradermal Injection?
An intradermal (ID) injection is a method of administering a substance by injecting it into the dermis, which is the layer of skin located just below the epidermis. This layer of skin is relatively thin and has fewer blood vessels compared to the subcutaneous tissue or muscle, which allows for slower absorption of the injected substance. This characteristic makes the intradermal route particularly suitable for tests where a localized reaction needs to be observed.
Why are Intradermal Injections Used?
The primary reason for using intradermal injections is to deliver medications or substances that require slow absorption and a localized effect. The dermis is rich in immune cells, which makes this route effective for certain diagnostic tests that assess the body's immune response to a substance.
Common Applications in Healthcare
Intradermal injections have several important uses in medical practice:
Tuberculosis (TB) Testing
One of the most common applications is the Mantoux tuberculin skin test, used to screen for latent tuberculosis infection. A small amount of tuberculin purified protein derivative (PPD) is injected intradermally, and the site is then observed for a reaction (induration) after a specific period.
Allergy Testing
Intradermal tests are frequently used in allergy diagnosis. Small amounts of potential allergens are injected into the skin, and healthcare professionals observe for localized reactions such as redness, swelling, or itching, which can indicate sensitivity to a particular substance.
Certain Vaccinations
While many vaccines are given via other routes, some, like the JYNNEOS vaccine for mpox, can be administered intradermally, often using a smaller dose due to the immune cell presence in the dermis.
Local Anesthetics
In some procedures, a local anesthetic might be administered intradermally to numb a small area of skin before a more invasive procedure.
General Principles of Administration (for trained professionals)
Administering an intradermal injection requires careful technique to ensure the substance is delivered to the correct skin layer. Key aspects include using a small-gauge needle and a tuberculin syringe to control the small volume of medication. The injection is typically given at a very shallow angle to deposit the substance just under the skin's surface. A characteristic sign of a successful intradermal injection is the formation of a small, raised area called a wheal or bleb at the injection site. Choosing appropriate sites, such as the inner forearm or upper back, is also important to minimize discomfort and ensure accurate test results.
Intradermal vs. Other Injection Types
Understanding the differences between injection types highlights why the intradermal route is chosen for specific purposes. The depth of injection and the rate of absorption are key distinctions:
| Aspect | Intradermal (ID) | Subcutaneous (SC) | Intramuscular (IM) |
|---|---|---|---|
| Injection Depth | Dermis | Fatty tissue | Muscle |
| Absorption Rate | Slowest | Slow | Fastest |
| Common Uses | TB, allergy tests | Insulin, some vaccines | Vaccines, antibiotics |
Conclusion
Intradermal injections are a valuable technique in healthcare for specific diagnostic tests and vaccinations, relying on the dermis's slow absorption rate to produce localized effects. This method, when performed by trained healthcare professionals, is crucial for accurate allergy and TB screening and the administration of certain vaccines. The formation of a wheal is a key indicator of correct administration. For detailed guidance on proper and safe injection techniques, healthcare professionals should always refer to current clinical guidelines and training.(https://www.cdc.gov/mpox/hcp/vaccine-considerations/intradermal-administration.html)
