Diagnosing tuberculosis

EBM Klinik protokolları

20.03.2017 • Sonuncu dəyişiklik 31.07.2015

PaulaMaasilta

Essentials

Even if tuberculosis has become rare in many countries it is important to bear the possibility of the disease in mind and start diagnostic investigations without delay if tuberculosis is suspected.
Pulmonary tuberculosis and lymph node tuberculosis are the most common forms of the disease.
In practice, only staining-positive pulmonary tuberculosis is infectious and triggers contact tracing.

In 2013 there were 269 diagnosed tuberculosis cases in Finland (5.0/100 000). 79% were pulmonary tuberculosis, of which 43% were sputum staining positive.
As tuberculosis has become rarer the relative proportion of infections caused by atypical mycobacteria has increased.

Near contacts to a patient with staining-positive pulmonary tuberculosis
Elderly persons (over 75 years of age)
Persons who have alcohol or drug abuse problems or who are socially exluded
Refugees and immigrants from countries with high incidence of tuberculosis
Patients with certain other diseases (HIV, diabetes, rheumatoid arthritis, malignancy, silicosis, severe renal failure)
Patients receiving immunosuppressive medication (antirejection drugs, TNF inhibitors, cytotoxic drugs, glucocorticoids)
Health and social care personnel
Prisoners

Staining and culture from repeated, consecutive specimens (sputum, urine), usually on three consecutive days
Mycobacterium tuberculosis can also be directly determined from a sample by rapid tests based on gene amplification .
- Most commercial tests have only been validated and licensed for DNA isolated from staining-positive sputum and/or culture. The tests usually are less sensitive for staining-negative sputum and other samples.
- It is advisable always to perform some DNA rapid test on a staining-positive sample in order to quickly check whether the causative agent is M. tuberculosis or an atypical mycobacterium.
Specimens
- Body excretions and fluids: sputum, urine, blood, CSF, pleural fluid, bone marrow, wound discharge
- Needle and aspiration samples
- Tissue samples (in a clean tube without formaldehyde)
The culture takes 4–6 weeks.

May be asymptomatic.
General symptoms: fatigue, poor appetite, weight loss, fever bouts, night sweats
Pulmonary symptoms: prolonged cough and mucus production, haemoptysis

Chest x-ray
Bacteriological samples: sputum staining and culture for tuberculosis on 3 consecutive days (result of staining is available in a few days, culture takes 4–6 weeks)
Tuberculin skin test (Mantoux) is used to support the diagnosis particularly in paediatric patients. Performing and interpreting of the test requires education and experience, and therefore the use of the test should be centralized to units with proper training.
- It is important to perform the tuberculin skin test as instructed .
- An induration with a diameter of less than 5 mm is interpreted as negative. An induration with a diameter of at least 15 mm is interpreted as a sign of latent or active tuberculosis infection both in vaccinated and non-vaccinated persons. If the diameter is between 5 and 14 mm the interpretation is dependent on e.g. the immunization status of the person; consult the national and international guidelines.
Laboratory tests based on gamma interferon production (IGRA = Interferon Gamma Release Assay) are a kind of “tuberculin tests performed in a laboratory”. A positive result does not distinguish active tuberculosis from latent tuberculosis infection, and therefore the diagnosis should be based on Mycobacterium culture and staining. IGRA tests are more specific than tuberculin skin tests.

Pneumonia (on the other hand, consider tuberculosis if pneumonia responds poorly to treatment)
Benign and malignant tumours of the lung
Metastases
Sarcoidosis
Eosinophilic pulmonary infiltrates
Pneumoconiosis
Fungal diseases
Atypical mycobacteria
Pulmonary abscess

Lymph nodes
Urogenital region
Central nervous system (the drug treatment differs from standard treatment and must be started urgently!)
Bones and joints
Pleura
Pericardium

A disseminated blood-borne form of tuberculosis
The chest x-ray may be normal at the initial stage. Computed axial tomography may be diagnostic in such cases.
A negative tuberculin test may be a sign of severe tuberculosis.
Consider miliary tuberculosis in elderly institutionalized patients with prolonged fever and an elevated serum alkaline phosphatase concentration.
In patients with AIDS a mycobacterial infection may have special features. Tuberculosis may be the first manifestation of an HIV infection.

The diagnosis is not considered.
Tuberculosis is treated as an other disease.
The symptoms of tuberculosis are thought to be an exacerbation of an underlying disease.

Mycobacteria-containing aerosol is most infective (coughing, suction of the airways).
In practice only pulmonary tuberculosis is infectious.
The disease is never transmitted by contaminated objects.
The infectiousness depends on the amount of mycobacteria in the sputum . If the bacteria are detected by staining, the risk of transmission is considerable. If bacteria are only detected by culture the risk of transmission is negligible, and no special measures are indicated (with the exception of organ transplant recipients, childcarers, etc.). In addition, a person who has staining-negative sputum but in whom imaging studies of the lungs show a cavity can be considered infectious.