T.B is mainly a bacteriological diagnosis by Ziehl-Neelsen stained smear or culture on Lowenstien Jensen Media or Middle brook).
The culture on middle brook needs short duration (2-3 wks) PCR is also a recent methode .
1- Bacterial examination :
If -ve for 3times, this may indicates -ve T.B infection ?
• Mycobacteria is recognized by their surface lipids which makes them acid fast in the laboratory examination.
• Isolation of organism from
2-Radiological picture: (usually gives apical lesion)
* Cavity * Fibrosis * Consolidation
* Effusion * Collapse * Miliary shadow
• The test involves an intradermal injection of the purified protein derivative (PPD) of the bacilli.
• After 48-72 hours the injection site is examined for visible and palpable induration.
• Because of a possible cross reaction after exposure to other mycobacteria a single tuberculin test to determine sensitization to mycobacterium tuberculosis is considered positive only if the diameter of the induration at the skin test site measures :
* > 15 mm in immunocompetent individuals.
* > 10 mm in sick persons without depression of their immune system .
* > 5 mm in immunocompromised patients e.g (organ transplant recipients or patients with HIV infection).
2. If it becomes +ve in a child, this mostly indicates recent tuberculous infection !?
3. For contact with a case :
4. A repeatedly negative test after 6 weeks from the onset of symptoms may rule out tuberculosis !?
5. Tuberculin test is also positive in atypical mycobacterium infection .
* Specific PPD for (avium,kansasi) is the method to differentiate atypical mycobacterial infection from mycobacterium tuberculosis.
2- Immunocompromised patient (anergy) e.g. AIDS, Steroids, Cytotoxic, Sarcoidosis
3- Bad technique
4- Miliary T.B
5- Viral infection e.g measles ===> immunosuppression.
4- E.S.R :
- ESR is High in active T.B. (usually> 100)
- It is used in follow up
- Can rule out active T.B if it is normal !?
5- Blood picture
• Leucopenia with relative lymphocytes
• Anemia of chronic disease (normocytic, normochromic)
6- PCR : Recently it is an accurate technique(sputum - BM - CSF - urine).
7- Biopsy from the pleural, lymph nodes or solid lesion within the lung or from peritoneum, liver or bone marrow in disseminated disease .
Important links to related articles
-Pulmonary Tuberculosis def., causes, risks, pathology
- Manifestations of Pulmonary Tuberculosis (symptoms, signs)
- Miliary tuberculosis manifestations and investigations
- Complications of pulmonary tuberculosis
The culture on middle brook needs short duration (2-3 wks) PCR is also a recent methode .
1- Bacterial examination :
If -ve for 3times, this may indicates -ve T.B infection ?
• Mycobacteria is recognized by their surface lipids which makes them acid fast in the laboratory examination.
• Isolation of organism from
2-Radiological picture: (usually gives apical lesion)
* Cavity * Fibrosis * Consolidation
* Effusion * Collapse * Miliary shadow
3-Tuberculin skin test:
• It is used widely to screen certain high risk populations, particularly those who have been exposed to an infectious patients.• The test involves an intradermal injection of the purified protein derivative (PPD) of the bacilli.
• After 48-72 hours the injection site is examined for visible and palpable induration.
• Because of a possible cross reaction after exposure to other mycobacteria a single tuberculin test to determine sensitization to mycobacterium tuberculosis is considered positive only if the diameter of the induration at the skin test site measures :
* > 15 mm in immunocompetent individuals.
* > 10 mm in sick persons without depression of their immune system .
* > 5 mm in immunocompromised patients e.g (organ transplant recipients or patients with HIV infection).
Values of tuberculin test:
1. Positive test indicates recent or old infection or vaccination.2. If it becomes +ve in a child, this mostly indicates recent tuberculous infection !?
3. For contact with a case :
4. A repeatedly negative test after 6 weeks from the onset of symptoms may rule out tuberculosis !?
5. Tuberculin test is also positive in atypical mycobacterium infection .
* Specific PPD for (avium,kansasi) is the method to differentiate atypical mycobacterial infection from mycobacterium tuberculosis.
Causes of false -ve tuberculin test:
1- Before 6 weeks (preimmune period)2- Immunocompromised patient (anergy) e.g. AIDS, Steroids, Cytotoxic, Sarcoidosis
3- Bad technique
4- Miliary T.B
5- Viral infection e.g measles ===> immunosuppression.
4- E.S.R :
- ESR is High in active T.B. (usually> 100)
- It is used in follow up
- Can rule out active T.B if it is normal !?
5- Blood picture
• Leucopenia with relative lymphocytes
• Anemia of chronic disease (normocytic, normochromic)
6- PCR : Recently it is an accurate technique(sputum - BM - CSF - urine).
7- Biopsy from the pleural, lymph nodes or solid lesion within the lung or from peritoneum, liver or bone marrow in disseminated disease .
Important links to related articles
-Pulmonary Tuberculosis def., causes, risks, pathology
- Manifestations of Pulmonary Tuberculosis (symptoms, signs)
- Miliary tuberculosis manifestations and investigations
- Complications of pulmonary tuberculosis