The Fine Art of Administering a Tuberculin Skin Test

Tuberculosis is an airborne disease with serious medical consequences. It is caused by the bacterium Mycobacterium tuberculosis, which belongs to a group of closely related organisms in the M tuberculosis complex. Once an individual is infected with it, the disease develops primarily in the lungs. Only the active form of tuberculosis is contagious, with signs and symptoms that include fatigue, fever, night sweats, chills, loss of appetite, unintentional weight loss, hemoptysis, shortness of breath, and cough that may last ≥3 weeks.¹

Approximately 13 million Americans have a latent tuberculosis infection, which usually results when immunocompetent individuals are exposed to M tuberculosis.² These individuals are not contagious, nor do they exhibit symptoms. However, latent tuberculosis may progress into an active case. Thus, screening for tuberculosis is a primary prevention tool that should be performed regularly.

During 2013 through 2015, for the first time in 23 years, the incidence of tuberculosis cases leveled off after decreasing each year.³ The same data showed that the majority of individuals infected with tuberculosis were clustered in California, Florida, New York, and Texas. In light of the persistence of this curable pathogen, healthcare providers should advocate for increasing awareness and encouraging screening for tuberculosis infection in appropriate settings. Presently, the vast majority of clinics use the Mantoux test to screen for cases of tuberculosis.

Injection Technique

Proper injection technique is essential when testing for tuberculosis. The Mantoux test is administered in the intradermal layer of the volar aspect of the forearm approximately 4 inches below the antecubital area. The bevel edge of the needle should be facing up and then inserted to inject 0.1 mL of tuberculin purified protein derivative (PPD). Proper injection technique should produce a small elevation (wheal) at the injection site. A reaction occurs when both induration and erythema are present 48 to 72 hours after administration. The diameter of the induration is measured in millimeters at the widest part. Erythema without induration is not considered significant.⁴

A significant reaction indicates that a patient has been exposed to M tuberculosis recently or in the past, or has been vaccinated with bacilli-containing Calmette-Guerin vaccine, which is effective in up to 80% of those who receive it.⁵ The vaccine is routinely used in Europe and Latin America but not in the United States. A positive tuberculin skin test (TST) does not mean active disease is present. Likewise, a negative TST does not exclude tuberculosis infection completely. In addition, an adequate immune response to produce a positive TST will not occur in a person who is immunocompromised.

Reading of the TST should be conducted within 48 to 72 hours. The provider should palpate for induration to ensure that only induration and not injection is being measured. An induration measuring ≥15 mm in greatest diameter indicates a positive test in individuals with no known risk factors for tuberculosis, an induration ≥10 mm indicates a positive test in recent arrivals from high-risk countries, and an induration ≥5 mm represents a positive test in an individual with HIV or immunosuppression, or someone who recently has been exposed to active tuberculosis.⁶⁴  

For many years, the Centers for Disease Control and Prevention (CDC) has emphasized the importance of implementing proper techniques for administration of the Mantoux test. More specifically, healthcare providers are advised to repeat the Mantoux test on the opposite arm if the initial PPD does not yield a wheal at the injected site.⁷ Common misconceptions exist among clinicians concerning the significance of creating a wheal when administering a TST. As an example, a newly graduated nurse posted comments in an online nursing forum seeking validation from other forum members concerning her experience administrating a TST on a patient without a resultant wheal (Table).

Table. Responses Given by Forum Members

“It happens sometimes. It will be fine.”8

“If they have tuberculosis, it will still react. I wouldn’t worry too much. You probably just went a bit too deep.”9

“We were taught in school that results won’t be valid without a wheal. I guess what they say is true about things being different in the ‘real world’ of nursing!”10

“…Ideally you get a wheal, but if someone has tuberculosis they will react.”11

This article originally appeared on Clinical Advisor