Intradermal injections can be used for the diagnosis of tuberculosis, for allergy testing, and for local anesthesia. The rationale for injecting into the dermis, as opposed to the subcutaneous layer of the skin or the muscle, is that it can elicit localized effects while limiting the systemic dispersion of the injected substances. Injecting into the dermis can also elicit specific immune responses that are easily detected by inspection and palpation. The procedure is quickly learned and is performed by a physician, nurse, or physician’s assistant. Intradermal injections can be used with children in any age group.

The classic and most common application of this procedure is the intradermal injection of mycobacterium derivatives to diagnose previous mycobacterium infection. This procedure, first described by Mantoux in 1908 (1), is currently the most widely used and cost-effective tool for diagnosing tuberculosis. Because of the recent resurgence of tuberculosis in the United States, this diagnostic procedure is commonly used in the emergency department (ED) setting.

The skin is composed of three basic layers (see Fig. 128.1)—the epidermis, the dermis, and the subcutaneous tissue. The epidermis is a thin, superficial layer composed of an outer layer of dead, keratinized epithelial cells and an inner cellular layer. The dermis lies just beneath the epidermis and contains blood vessels, connective tissue, hair follicles, and sebaceous glands. The deeper subcutaneous layer contains mostly fat. This layer supports the blood vessels, nerves, and lymphatics that supply the more superficial layers. Sweat glands and roots of hair follicles also are found in the subcutaneous layer.

The tuberculin tests (tine and Mantoux) are the prototypes of a cell-mediated immune response (type IV hypersensitivity reaction). In the nonimmunocompromised patient, exposure to an antigen (e.g., Mycobacterium tuberculosis) results in the development of sensitized lymphocytes. Re-exposure to the antigen (as in intradermal injection) causes these cells to release mediators at the site of re-exposure, which results in induration and erythema (a positive test). If no reaction occurs, the patient was not exposed to a significant load of the antigen previously or the patient is anergic. This type of reaction, called a “delayed hypersensitivity skin test,” usually manifests within 48 to 72 hours. Table 124.1 lists other potential antigens available for intradermal skin testing.

Other antigens such as antibiotics result in an immediate hypersensitivity reaction mediated by IgE on presensitized mast cells in the dermis (type I hypersensitivity reaction). This type of reaction can detect sensitivity to a host of other antigens, including other drugs, microorganisms, pollens, animal dander, and helminths. A positive response is manifested by the triple response of Lewis et al. (2). Initially the skin becomes pale, followed by an erythematous flare and then a slight swelling or induration described as a “wheal.” This dermal reaction to histamine usually begins within 5 minutes of allergen exposure and peaks at approximately 30 minutes. Occasionally, a late phase reaction occurs 3 to 24 hours later and manifests as ill-defined edema.

The tuberculin skin test is based on the observation by Robert Koch that infection with M. tuberculosis caused cutaneous reactivity to tuberculin, the heat-killed, purified protein derivative (PPD) from cultures of M. tuberculosis. When tuberculin is introduced into the dermis with a syringe, the test is called a “tuberculin skin test” (TST) or “Mantoux test.” This test is currently the only recommended skin test for detecting
tuberculosis. It is indicated acutely in suspected mycobacterial infection or in patients with a significant tuberculosis exposure (Table 124.2). This diagnosis should be considered in children with chronic cough, pneumonia (especially of the upper lobes), adenopathy (particularly of the hilum) or adenitis (especially of the head or neck), or meningitis. Tuberculosis can involve virtually any body system, including the lungs, central nervous system, gastrointestinal system, cardiovascular system, bones, joints, skin, and eyes. In the primary care setting, a risk assessment questionnaire (Table 124.3) is used to identify patients with risk factors for TB who should be tested (3). TST is not indicated routinely for low-risk populations. The screening multiple puncture tests (including the commercial brands Monovacc, Aplitest, and Tine) are no longer recommended for the diagnosis of tuberculosis due to a high rate of false-positive responses (approximately 20%) and false-negative responses (up to 10%) (4). The only absolute contraindication for intradermal tuberculin placement is a severe skin reaction with prior testing. The patient will give a history of a bullous or necrotic-type reaction. Upon examination of the patient, it is also likely that residual scarring from such a reaction will be evident.