How is it diagnosed

The main tools for diagnosing pulmonary TB are sputum smear microscopy, chest X-ray, and culture of Mycobacterium tuberculosis bacilli.
Sputum microscopy is easy to perform at the peripheral laboratories, not expensive It gives highly specific results with very low inter and intra-reader variations. Therefore it is considered as primary diagnostic tool for case detection in RNTCP.
X-ray as a diagnostic tool is sensitive but less specific with large inter and intra reader variations. It is considered an important “supportive” tool for diagnosis of smear negative pulmonary TB
Culture of Mycobacterium tuberculosis bacilli is very sensitive and highly specific test but it is expensive and it requires a specialized laboratory set-up. But the results are available only after several weeks. Hence it is not employed for routine patient management.
Tuberculosis may also affect organs other than the lungs. This form of the disease is called extra-pulmonary tuberculosis. Methods for the diagnosis of extra-pulmonary cases depend on the system that is affected.

Sputum Microscopy
Simple not expensive, requires minimum training.
Specific with low inter-reader variation.
Can be used for diagnosis, monitoring and defining cure.
Feasible at peripheral health institutions
Correlates with infectivity in undiagnosed pulmonary TB cases

X-ray
Supportive to microscopy
High inter-reader variation
No shadow is typical of TB
10–15% culture-positive cases remain undiagnosed
40% patients diagnosed as having TB by X-ray alone may not have active TB disease.
Tuberculin test may be useful as an additional tool for diagnosing pediatric TB.

Process of Diagnosis:

Patients with chest symptoms and other symptoms suggestive of TB, consult medical staff at governmental, non-governmental or private general health facilities. The Medical Officer (MO) at the health facility screens the patients. All outpatients with a cough of 2 or more weeks are to be considered as tuberculosis suspects.

Using the RNTCP laboratory form for sputum examination, the MO sends the suspects for sputum examination. In Medical Colleges and other hospitals, indoor-patients suspected of TB are also to be referred by the treating physician using the same RNTCP laboratory forms for sputum examination. In the laboratory the patient receives sputum containers with instructions to provide sputum samples, which are then subjected for sputum examination. If the health facility is not a DMC then the patient may be referred to the nearest DMC or else the patient’s sputum is collected and transported to the DMC.

Two sputum samples are collected over two consecutive days:
Spot sample on the first day, and
One early morning sample on second day
Following Diagnostic algorithm is followed to arrive at the diagnosis of TB and further categorization of patients for treatment.

Pediatric TB: The screening criterion for diagnosis of pediatric TB is a combination of
1. Clinical presentation
2. Sputum examination wherever possible
3. Chest X ray (PA view)
4. Mantoux test (1 TU PPD RT23 with Tween 80, positive if induration >10mm after 48-72 hours).
5. History of contact with TB patient

Following algorithm is employed to arrive at diagnosis of TB in children:

The use of currently available scoring systems is not recommended for diagnosis of pediatric TB patients.