Q. The procedure shown here is known as?
A) Schick test.
B) Dick test.
C) Mantoux (Tuberculin Skin) Test.
D) Patch test.
✓ The Correct Answer is: C) Mantoux (Tuberculin Skin) Test.
The image shows the Mantoux test, also known as the Tuberculin Skin Test (TST). It is one of the oldest and most widely used screening tests for Mycobacterium tuberculosis infection.
Although newer blood-based tests are now available, the Mantoux test continues to play an important role in everyday clinical practice, especially in countries where tuberculosis remains common.
The test is performed by injecting 0.1 mL of purified protein derivative (PPD), containing 5 tuberculin units (TU), intradermally on the volar aspect of the forearm using a fine needle.
A correctly performed injection produces a small, raised wheal measuring approximately 6–10 mm in diameter.
Unlike many skin tests, the Mantoux test is not interpreted immediately. The patient should return 48–72 hours later, when the induration (firm swelling) is measured across its widest diameter. Erythema (redness) is ignored, as only the palpable induration has diagnostic value.
∆ Principle of the Test
The Mantoux test is based on a Type IV (delayed) hypersensitivity reaction mediated by T-lymphocytes.
Individuals who have previously been sensitized to Mycobacterium tuberculosis develop a localized inflammatory response at the injection site.
Importantly, a positive Mantoux test indicates prior sensitization to mycobacterial antigens.
It does not differentiate between latent tuberculosis infection, active tuberculosis disease, or previous BCG vaccination, making clinical correlation essential.
∆ Interpretation
Interpretation depends on the patient's risk factors and immune status rather than a single cut-off value.
≥5 mm is considered positive in individuals at very high risk, such as people living with HIV, recent contacts of infectious TB patients, organ transplant recipients, or those receiving significant immunosuppressive therapy.
≥10 mm is positive in individuals with moderate risk, including healthcare workers, patients with diabetes, chronic kidney disease, or people from high-prevalence regions.
≥15 mm is generally considered positive in individuals without known risk factors.
∆ Clinical Practice
In routine clinical practice, the Mantoux test is commonly used to-:
1. Screen healthcare workers for tuberculosis exposure.
2. Evaluate close contacts of patients with infectious pulmonary tuberculosis.
3. Detect latent tuberculosis infection (LTBI) before initiating biologic agents, chemotherapy, or long-term corticosteroid therapy.
4. Assess patients before organ transplantation or other forms of immunosuppression.
5. Support the diagnosis of tuberculosis when interpreted alongside clinical findings and radiological investigations.
However, the Mantoux test should never be used alone to diagnose active tuberculosis.
Patients with symptoms suggestive of active TB require microbiological confirmation with sputum examination, nucleic acid amplification tests, culture, and appropriate imaging.
∆ Other Options-:
Schick test was historically used to determine susceptibility to diphtheria.
Dick test was used to assess susceptibility to scarlet fever caused by Streptococcus pyogenes.
Patch test is employed in the diagnosis of allergic contact dermatitis and evaluates delayed hypersensitivity to allergens rather than tuberculosis.
∆ High-Yield Exam Pearls:
Test name: Mantoux (Tuberculin Skin Test).
Injection: 0.1 mL PPD (5 TU), intradermally.
Site: Volar aspect of the forearm.
Reading: 48–72 hours.
Measure: Induration only, not erythema.
Immunological basis: Type IV delayed hypersensitivity reaction.
Most common use: Screening for latent tuberculosis infection.
✓ One-Liner to Remember:
"Mantoux = Intradermal PPD + Read at 48–72 hours + Measure induration, not redness."
✓ Take-Home Message:
The Mantoux (Tuberculin Skin) Test remains a valuable and widely used tool for detecting latent tuberculosis infection, particularly in high-risk individuals and before immunosuppressive therapy.
A positive result reflects prior immune sensitization to Mycobacterium tuberculosis antigens and must always be interpreted in the context of the patient's history, risk factors, BCG vaccination status, and clinical findings.
Understanding its principle, procedure, interpretation, limitations, and real-world clinical applications is essential for success in MBBS, NEET PG, INICET, FMGE, USMLE, and PLAB examinations as well as for safe clinical practice.
