Primary Complex

Primary Complex

Write about laboratory investigation done in case suffering from pulmonary tuberculosis.
Or
Write a short note on laboratory diagnosis of tuberculosis.
Or
Write a short note on the primary complex.
Answer:

The laboratory diagnosis of tuberculosis is done by:

Laboratory diagnosis of tuberculosis Diagnosis

1. Demonstration of AFB on microscopic examination of a diagnostic specimen (sputum or tissue): Smears or tissue slides stained by Ziehl-Neelsen stain are examined for acid-fast bacilli.

This method has a relatively low sensitivity in confirmed cases of pulmonary tuberculosis. Auramine-rhodamine staining and fluorescence microscopy can improve sensitivity to a certain extent.

Three sputum specimens preferably collected early in the morning should be submitted to the laboratory for AFB smear and mycobacterial culture.

2. Culture: Besides sputum and tissue other specimens which can be used for culture are body cavity fluids, urine or gastric lavage fluid.

Specimens may be inoculated onto egg or agar-based medium, For Example. Lowenstein- Jensen or Middle- brook 7H10 media and incubated at 37°C.

M. tuberculosis grows slowly (4-8 weeks). A presumptive diagnosis can be made based on colony pigmentation and morphology; however, biochemical tests are must for species recognition.

Primary complex in tuberculosis

3. Molecular typing: M. tuberculosis is isolated and species identification is done by molecular methods or high-pressure liquid chromatography of mycolic acids (reducing the time required for a confirmation to 2-3 weeks). Polymerase chain reaction, i.e. PCR is the conformational method.

4. Tuberculin sensitivity test: It is based on the principle that M. tuberculosis in a concentrated liquid culture medium i.e. purified protein extract can elicit a skin reaction when injected subcutaneously into patients with tuberculosis.

A person is given the tuberculin and asked to return within 48-72 hours to have a trained health care worker to look for a reaction on the arm (swelling, induration and erythema) and measure its size.

Redness by itself is not considered part of the reaction. The lack of mycobacterial species specificity, the subjectivity of interpretation and batch-to-batch variations limit the usefulness of protein purified derivative.

5. In vitro assays that measure T cell release of IFN­? in response to stimulation with the highly tuberculosis­specifi antigens ESAT­6 and CPP­10:

These are commercially available assays (Interferon-? release assay or IGRA) IGRAs are more specific than the tuberculin sensitivity test as a result of less cross-reactivity due to BCG vaccination and sensitization by non-tuberculous mycobacteria.

Ghon complex TB

IGRAs also appear to be at least as sensitive as the tuberculin-sensitive test for active tuberculosis.

6. Complete hemogram: It shows lymphocytosis and raised ESR.

7. Fine needle aspiration cytology: This is done in the enlarged peripheral lymph node and is an easy way for confirm of the diagnosis

8. Immunohistochemistry: Immunohistochemical stain with anti-MBP 64 antibody stain can be used to demonstrate the organism.