Overview
The Mantoux test is a widely used screening tool for tuberculosis that assesses the body’s immune response to Mycobacterium tuberculosis proteins. It is performed using purified protein derivative, a glycerol extract of tubercle bacilli containing non-specific proteins. The test helps in identifying latent tuberculosis infection as well as supporting the diagnosis of active tuberculosis when interpreted along with clinical findings and other investigations. It does not distinguish between latent and active disease on its own but indicates prior exposure or infection.
Symptoms
The Mantoux test itself does not produce disease-related symptoms. The local reaction at the injection site is the primary observable response. This includes the development of induration, which is a raised, firm area at the site of injection. Redness or erythema may be present but is not considered for interpretation. Systemic symptoms are not expected as part of the test response and, if present, usually relate to underlying tuberculosis or other medical conditions rather than the test itself.
Causes
A positive Mantoux test result occurs due to a delayed-type hypersensitivity reaction mediated by T lymphocytes in individuals previously sensitized to tuberculosis antigens. This sensitization may be due to latent or active tuberculosis infection, prior exposure to Mycobacterium tuberculosis, or vaccination with Bacille Calmette Guérin. False positive reactions may occur due to non-tuberculous mycobacterial exposure, while false negative reactions can result from recent infection, immunosuppression, malnutrition, corticosteroid therapy, or certain systemic illnesses.
Risk Factors
Risk factors influencing Mantoux test interpretation include immune status, recent exposure to tuberculosis, age, nutritional status, and prior BCG vaccination. Individuals at higher risk include people living with HIV, organ transplant recipients, immunosuppressed patients, recent contacts of tuberculosis patients, healthcare workers, residents of high-risk settings, and individuals with chronic medical conditions such as diabetes or renal disease. Improper administration, incorrect reading time, or errors in measuring induration may also affect results.
Prevention
Prevention of misinterpretation relies on the correct administration, reading, and interpretation of the Mantoux test. The standard dose of purified protein derivative should be injected intradermally, and results must be read between 48 and 72 hours by measuring induration in millimeters. Interpretation should always be based on the size of induration and the individual’s risk factors rather than redness. Awareness of factors causing false positive or false negative results is essential. When used appropriately, the Mantoux test supports early identification of tuberculosis infection, enabling timely evaluation, follow-up, and preventive or therapeutic interventions.
