Secondary tuberculosis:

The post primary tuberculosis is due to reactivation of latent infection or may be due to exogenous reinfection.It is characterized by chronic tissue lesions, the formation of tubercles,caseation and fibrosis.Important features of secondary tuberculosis are the presence of caseous necrosis and cavities.This may rupture and spread mycobateria through out the body.If it breaks in Air way.it will release tubercles bacilli in sputum.

The complication of pulmonary tb are pleural fibrosis,empyema adrenal insufficiency, massive haemoptysis and Hypercalcemia.

LABORATORY DIAGNOSIS:

PULMONARY TB:

SPECIMEN,

Sputum which consists of pus and mucous secretion coughed up from the lung.Laryngeal swabs or bronchial washing when sputum is not available.Gastric lavage is collected only in case of small children who tend to swallow the sputum.

Microscopy,

The sputum smear is prepared and stained by the ziehl neelsan technique.under the oil immersion objective,AFB are seen as bright red rods with blue background.Smears should be examined for at least 300 oil immersion fields before reporting it as negative.Smears can also be stained by sensitive stain like auramine phenol or auramine rhodamine fluorescent dyes.

Concentration method:

If less number of bacilli is suspected, then the sputum can be concentrated.Important concentration method is petroffs method.culture,the concentrated specimen is inoculated onto LJ medium.A negative report is given if no growth occurs after 8-12 week.In general,a mycobacterium which is slow growing,non pigmented,niacin positive acid fast bacillus is taken as M.tuberculosis.Tuberculin testing demonstration of hypersensitivity to tuberculoprotein is a standard procedure.

Molecular techniques,the technique available are hybridization techniques with nucleic acid probes , polymerase chain reaction,DNA finger printing, transcription mediated amplification.

Chromatography, The mycolic acid in the call wall of mycobacterium can be detected by High pressure liquid chromatography and be identified to the species level.

Extra pulmonary tuberculosis:

The problem encountered in extra pulmonary TB is the less number of tubercule bacilli in the lesion.The sample are most of the time concentrated and are cultured to identify the tubercle bacilli.

Tuberculin test principles of this test is delayed type four hypersensitivity reaction and is based on the fact that tubercle bacilli infected patient will develop hypersensitivity reaction to the protien of the organism.Mantoux test is the routinely used tuberculin test.A 0.1 ml of tuberculin antigen containing 5 TU is injected intradermally on the flexor aspects of the forearm with help of a tuberculin syringe.Tge test result is read 48-72 hours after injection.Tge reading is based on the presence or absence of induration.Induration of diameter 10 mm or more is considered postive.