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TB Test / PPD Test, TB Vaccine, TB Treatment

How TB test is done for the Patients

Testing the Sputum of patients

TB Test is done by taking out the sputum samples from the patient during a coughing episode and growing them in culture media (It is a nutritional media that supports the growth of microorganisms).’

The growth can be either Present (Positive) or Absent (Negative)

Positive culture:- It means growth of Mycobacterium tuberculosis (a bacteria that cause TB) colonies on culture media will be seen.
Negative culture – No growth will be seen.


Biopsy – A small sample of Tissue/Fluid will be taken from the site which is thought to be affected by Tuberculosis.
A biopsy is taken by the doctors only if the tuberculosis is not present in the lungs.


PPD Test or Tuberculin skin test is performed for testing TB 

TB skin test will give you some clue about the TB Germs in your body. It is also called as Mantoux test.
Reagents for TB skin test includes Old tuberculin and Purified Protein Derivative (PPD).  They are injected into your skin to get the results.

TB Test / PPD Test procedure?

TB test is performed by experts by injecting a small amount of Tuberculin(PPD) into the skin of the lower part of the forearm. 

What will the skin look like with the Positive TB/ Mantoux test?

The site of injection is examined by experts after 48 -72 hours and interpreted by them as follows:
The Positive TB Test confirms the presence of Edema (swelling) in 10mm diameter or Redness is seen at the site where the injection was given.

What does a Positive TB test indicate?

TB positive skin test can indicate past infection with microorganisms but does not tell about the presence of the active stage of the disease.
There can be False Positive or Negative Results


TB false-positive test will occur in presence of atypical Mycobacteria (species of Mycobacterium other than classic Mycobacterium tuberculosis)


This test means that the patient has the disease but the TB test skin shows negative.

TB skin tests become False negative in the following conditions:

  • Miliary tuberculosis (spread of mycobacterium tuberculosis to different sites of the body through the blood)


Other tests for TB

  • Interferon-gamma release assay: It is a blood test done worldwide. It is based on the fact that the body’s immune cells will release chemicals known as Interferons (The markers of Mycobacterium tuberculosis) when reacting with specific antigens of Mycobacterium. Labs measures these chemicals.
  • Polymerase chain reaction(PCR): It is a rapid method in diagnosing Tuberculosis.

TB vaccines

  • BCG vaccines
    Full name- Bacillus Calmette–Guérin  
  • It should be given soon after birth to protect infants and children from Tuberculosis.
  • BCG vaccine is available on the market in liquid as well as freeze-dried form (commonly used).
  • BCG vaccine is also believed to protect from serious forms of Tuberculosis like meningeal (meninges are the coverings of the brain), skeletal and miliary (spreading form of TB)

Contraindications of BCG Vaccine

BCG Vaccine is contraindicated in patients with AIDS, Measles, whooping cough(kaali khansi), Dermatitis (skin swelling), and patients on Steroids.

TB Treatment

Plan for treatment of TB has two phases –

  1. Intensive phase
  2. Continuous phase 

Intensive phase – The patients are prescribed four to six drugs daily for 2 months. The Intensive phase aims to kill the bacilli rapidly so that TB cannot spread by contact.

Continuous phase– The patients are prescribed three to four drugs daily for 4 months. The continuous phase aims to eliminate the Bacteria and prevent them from reoccurring.


What to do in patients with Multidrug resistance TB?

The treatment Regime in Multidrug-Resistant TB is as follows

Intensive phase                             B.Continuous phase
Drugs are taken for 6-9 months.  Drugs are taken for 18 months.

Pyridoxine (Vitamin B6) should be prescribed in patients with MDR TB in addition to other antitubercular 4 or 5 drugs to avoid the development of peripheral neuropathy. (Study)

Have a look at the D-Dimer test and find out why it is used in COVID Patients

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