Mantoux Test (TT)

What sample is needed for the Mantoux test?

• This test is done on the patient’s skin.

What are the indications for the Mantoux test?

1. To diagnose a suspected case of tuberculosis.
2. Screening of people at risk, such as:
   1. Health worker.
   2. Immigrants to a high-risk area.
   3. IV drug users.
   4. Patients at increased risk of developing active TB.
3. So, this TT should target high-risk groups, which is called targeted tuberculin testing, rather than low-risk people, which is called screening testing.

What is the epidemiology of Mycobacterium Tuberculosis?

1. Tuberculosis is the second leading cause of death in the world.
   1. Nearly 3 million people die each year.
   2. 7% of all deaths occur worldwide.
   3. The global epidemic may become worse because of drug-resistant organisms and HIV patients.
2. Mycobacteria are widely distributed worldwide. They are called acid-fast bacilli because they resist decolorization after mordanting with strong acid.
   1. This staining property relates to the cell wall’s high lipid content.
   2. The acid-fastness results from the formation of complexes between the dye and mycolic acid, one of the cell wall lipids.

What are the laboratory characteristics of Mycobacterium tuberculosis?

1. They are weakly Gram-positive organisms.
2. M. tuberculosis measures 0.2 to 5.0 µm bacilli.
3. These are slender, beaded bacilli and non-sporing organisms.
4. It is an obligate aerobe.
5. It grows in high O2 tension (pO₂) areas, such as lung apex tissue.
6. It is a slow-growing organism that needs 1 to 2 weeks or more to grow.
7. It has high cell-wall lipid content, such as mycolic acids, and is impervious to Gram stains.
   1. Smears are treated with concentrated carbol fuchsin for 10 to 20 minutes, which acts as a mordant by heating, and then decolorized with 20% sulphuric acid+ alcohol; now, bacilli will have a bright red color.

What are the culture media for Mycobacterium Tuberculosis?

1. These bacteria need highly enriched media, Lowenstein-Jensen medium. These bacteria do not grow on ordinary media.
2. Lowenstein-Jensen medium contains whole eggs, asparagine, glycerol, and malachite green, which inhibits contaminant growth.
3. The specimen is incubated at 37 °C for 2 to 3 weeks, but the culture should be kept for 6 to 8 weeks.
4. Nowadays, these bacteria are identified under fluorescent microscopy.
5. These are divided into two groups:
   1. Rapid growers, which form colonies in 2 to 3 days.
   2. Slow growers, which take 2 to 3 weeks.
6. The medically important mycobacteria are:
   1. M. tuberculosis.
   2. M. bovis.
   3. M. leprae.
   4. Atypical mycobacteria.
7. Mycobacterium tuberculosis causes a slowly progressive chronic infection, usually of the lungs.
   1. However, this disease can involve other organs.
   2. The primary source is the lung secretions, so-called open disease.

Mantoux test:

What is the principle of the Tuberculin sensitivity test (TT) or Mantoux test?

1. The Tuberculin test (TT) is important in diagnosing and preventing tuberculosis.
   1. This test is more sensitive than a chest X-ray.
2. This test is done on the patient, in which purified protein derivatives (PPD) are stabilized by Tween 80 (polysorbate 80-coated nanoparticles) and injected into the skin (Intradermal).
3. The standard test material is intermediate-strength, 5 tuberculin units, PPD.
4. Lymphocytes recognize PPD as an antigen and produce a type IV, cell-mediated reaction.
5. There will be a local inflammatory reaction in a person who has TB or has had past exposure to TB.
6. This test causes a severe reaction in active TB or in vaccinated patients. The skin may slough.

What is the basis for the Mantoux test (TT)?

1. It tests for infection with Tuberculosis.
2. It shows sensitivity to the TB antigen.
3. Memory T-cells recognize the antigen.
4. It produces a delayed type IV hypersensitivity reaction (delayed cellular immune response).

How would you read the Tuberculin test (TT) or Mantoux test:

1. Read the test area 48 to 72 hours after the injection.
2. The negative case is when there is no induration.
3. In positive cases, induration appears at the injection site within 48 to 72 hours.

What are the criteria of the American Thoracic Society and CDC?

1. They suggest the following criteria for different population groups:
2. Induration <5 mm in diameter is seen in:
   1. HIV patients or those in an immunodeficiency state.
   2. Or a patient with a CMI defect.
   3. Close contact with an active TB case.
   4. The patient had an X-ray finding of old TB.
   5. Patients with fibrosis or calcification in the lung suggest previous pulmonary tuberculosis.
3. Induration >10 mm in diameter is seen in:
   1. I/V drug users.
   2. Nursing home residents.
   3. Travelers from endemic or high-risk areas for tuberculosis, prisoners, homeless individuals, I/V drug abusers, and other chronically ill patients.
   4. A worker in the home care facility.
   5. Malnutrition, postgastrectomy, steroid use, and Diabetes.
4. Induration >15 mm in diameter is seen in:
   1. Patient with active TB.
   2. All patients who don’t fulfill the above criteria.
5. A booster reaction may be mistaken for conversion among hospital workers or others, so repeated testing is needed.
6. If the primary reaction is negative, or the result is in doubt, give the second dose after one week.
7. If the induration increases by more than 6 mm next year, it may suggest a new tuberculous infection.

What are the contraindications for the Tuberculin and Mantoux skin tests (T T)?

1. A patient who has active TB will have a very severe reaction.
2. A patient who has been vaccinated with Bacillus Calmette-Guérin (BCG).
3. No use in a malnourished patient.

Where will you see a positive Tuberculin (Mantoux skin test, TT)?

1. An active case of TB.
2. Other types of Mycobacterial infection.

Where will you see a negative Tuberculin or Mantoux skin test (TT)?

1. An immunocompromised, chronically ill patient.
2. The patient was not exposed to TB.
3. It is found that 20% of the HIV-negative and 40% of HIV-positive cases have tuberculosis.
4. Viral infections, including measles and rubella, can suppress tuberculin reactivity. However, this effect is transient.

• Because the tuberculin skin test has limited sensitivity and specificity, researchers are developing new methods, such as a sandwich-capture enzyme-linked immunosorbent assay, to diagnose Mycobacterium tuberculosis infection.

What are the causes of false-positive Mantoux test (TT)?

1. It is seen in BCG vaccination.
2. Infection with nontuberculous mycobacteria.

What are the causes of a false-negative Mantoux test (TT)?

1. Very recent TB infection.
2. In case of severe immunosuppression.
3. Severe illness.
4. Some advanced cases of TB.
5. In the younger age group.
6. Some of the advanced cases of TB.

Questions and answers:

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