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Information

Editors

PaulaMaasilta
TuulaVasankari

Diagnosing Tuberculosis

Essentials

  • Find out about potential national guidance or programme concerning tuberculosis.
  • 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 pulmonary tuberculosis is infectious and triggers infection tracing. In extrapulmonary tuberculosis, if aerosolization of any excretion into the air has taken place (e.g. when spraying an abscess or a lymph node with discharge), infection tracing may be warranted.

Epidemiology

Risk groups for tuberculosis

  • Individuals exposed to infectious tuberculosis
  • Elderly persons (especially those born before mass BCG vaccination in countries with high burden of tuberculosis at the time)
  • Drug- or alcohol-addicted individuals and socially exluded individuals
  • Immigrants from countries with high incidence of tuberculosis
  • People who have stayed in countries with high incidence of tuberculosis
  • Patients with factors increasing the risk of acquiring tuberculosis (HIV, diabetes, rheumatoid arthritis, malignancy, silicosis, severe renal failure)
  • Patients receiving immunosuppressive medication (antirejection drugs, TNF-alpha inhibitors, cytotoxic drugs, glucocorticoids)
  • People exposed to tuberculosis through their work
  • People who, if they become ill, may pose a danger to others through their work (working with children under school age, newborns or immunocompromised people)

Investigations

Bacteriological investigations

  • Tuberculosis nucleic acid detection provides the result faster, potentially reducing exposures and further infections. At the same time, information on resistance genes for main drugs can be obtained. However, nucleic acid testing should be accompanied by staining and culture which are important for determining drug sensitivities, for example.
  • Staining and culture from repeated, consecutive specimens (sputum [both examinations], urine [culture only]); usually a total of three samples is collected, on two consecutive days
  • Mycobacterium tuberculosis can also be directly determined from a sample by rapid tests based on gene amplification Rapid Diagnostic Tests for the Detection of Tuberculosis.
    • Performed on a cough sample is always recommended.
    • Can also be performed on specimens from body excretions and fluids.
    • A rapid test may also reveal potential drug resistance genes for rifampicin and isoniazid.
  • Specimens
    • Body excretions and fluids: sputum, urine, blood, CSF, pleural fluid, bone marrow, wound discharge, etc.
    • Needle and aspiration samples
    • Tissue samples (part of the sample in a clean tube without formaldehyde)
  • The culture takes 4-6 weeks.

Findings in tissue samples

  • Epitheloid cells
  • Langhans' giant cells
  • Caseous necrosis

Pulmonary tuberculosis

Symptoms

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

Organisation of diagnostics and treatment

  • Primary health care is responsible for the tasks listed below.
    • Identification of possible tuberculosis
    • Initiation of diagnostic investigations and referral to treatment
      • Chest x-ray is taken without delay. If there is sputum production, the collection of sputum samples should be started right away in the primary care (tuberculosis staining and culture 3 times).
      • If tuberculosis is diagnosed or strongly suspected, the patient is referred to specialist care without delay.
      • If a sputum sample stains positive or chest x-ray shows a clear cavity, the hospital should be contacted beforehand by phone and arrangements for isolation treatment agreed upon. Risk of contagion is recorded in the referral.
    • Implementation of supervised treatment Antitubercular Medication in Ambulatory Care
    • Carrying out of contact tracing

Diagnosis

  • Chest x-ray
  • Bacteriological samples: sputum staining and culture for tuberculosis using a total of 3 samples collected on 2 consecutive days
    • Result of staining is available in a few days, culture takes 4-6 weeks).
  • 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. They are used primarily in infection tracing and when considering starting treatment for latent tuberculosis.

Differential diagnosis

Extrapulmonary visceral tuberculosis

Common sites

  • Lymph node
  • Urogenital region
  • Central nervous system Meningitis in Adults
    • The drug treatment differs from standard treatment and must be started urgently!
  • Bones and joints
  • Pleura
  • Pericardium
  • Tuberculosis may be in any organ.

Miliary tuberculosis

  • A disseminated blood-borne form of tuberculosis
  • Miliary pulmonary changes may be found in imaging studies
    • Chest x-ray may be normal at the initial stage. High resolution computed tomography may be diagnostic in such cases.
  • Consider miliary tuberculosis in elderly institutionalized patients with prolonged fever and elevated ESR and serum alkaline phosphatase levels.
  • In patients with AIDS a mycobacterial infection may have special features. On the other hand, tuberculosis may be the first manifestation of AIDS.

Causes of misdiagnosis

  • The diagnosis is not considered.
  • The case is managed as another disease.
  • The symptoms of tuberculosis are thought to be an exacerbation of an underlying disease.

Infectiousness

  • Mycobacteria-containing aerosol is infective (coughing, suction of the airways).
  • In practice, only pulmonary tuberculosis is infectious, and even it is not transmitted through objects.
  • The infectiousness depends on the amount of mycobacteria in the sputum Exposure to Tuberculous Infection. If there are so many bacteria that they can be detected by staining, the risk of transmission exists beyond dispute. In addition, a person who has staining-negative sputum but in whom imaging studies of the lungs show a cavity can be considered infectious. Also the contacts of a staining-negative patient with pulmonary tuberculosis are examined if these are unvaccinated children or live in the same family with the patient.
  • Follow local requirements regarding reporting of the infection to the appropriate authorities.

    References

    • National tuberculosis programme 2020: Recommendations for the prevention, treatment, and monitoring of tuberculosis. Finnish Institute for Health and Welfare (THL), Ohjaus 7/2020. Abstract available in English, full report in Finnish at http://urn.fi/URN:ISBN:978-952-343-505-6.