Study Guide on Tuberculosis - M.M. Savula 2002

Diagnostic Methods for Tuberculosis
Laboratory Diagnostic Methods

The detection of Mycobacterium tuberculosis (MTB) is the most critical investigation for confirming the tuberculous nature of a disease. MTB is typically sought in sputum, bronchial washings, laryngeal swabs, induced sputum (obtained via inhalation of an irritant mixture consisting of a 15% saline solution and a 1% sodium bicarbonate solution), or material obtained during bronchoscopy. In cases of extrapulmonary involvement, pleural fluid, CEREBROSPINAL FLUID, urine, and sinus secretions are examined for MTB.

Sputum is the most common specimen used for MTB detection. It is collected in a sterile pocket sputum container in the morning, while fasting. The patient should brush their Teeth and rinse their Mouth with boiled Water or a 2% sodium bicarbonate solution, followed by a deep cough to expectorate material from the respiratory tract. The patient's name, initials, and the date are recorded on the label before the specimen is delivered to the laboratory. If the sputum cannot be submitted for examination within 2 hours, it must be preserved by adding an equal volume of a 2% boric acid solution.

If urine analysis for Mycobacterium tuberculosis is required, the specimen is collected in a sterile container in the morning, following proper perineal hygiene.

In clinical practice, specimens are most commonly examined for MTB using bacterioscopy or by culture on nutrient media.

Bacterioscopy allows for rapid results. Sputum smears are stained using the Ziehl-Neelsen method, which is based on the acid-alcohol fastness of the tuberculosis pathogen—the ability of MTB, once stained with fuchsin, to retain the dye even after prolonged exposure to acid or alcohol, while other microbial flora lose their coloration. Under the oil immersion lens of a Microscope, MTB appear as delicate red rods against a blue Background (Fig. 12 - see Appendix). A limitation of this method is that MTB are only detected when present in high concentrations (at least 50,000–100,000 per 1 ml of sputum). Therefore, the test is repeated at least three times. Bacterial shedding detected by simple bacterioscopy is considered massive and particularly hazardous. The bacterioscopy method is simple, accessible, and can be performed in hospitals, clinics, or outpatient centers. Currently, it is widely recommended for detecting open (Bacteria-shedding) forms of tuberculosis in outpatient settings among patients with a chronic cough. This is especially important for elderly or non-transportable patients, for whom sputum can be collected at home and delivered to the nearest laboratory.

The flotation (enrichment) method is slightly more accurate (by 10-15%) but more labor-intensive. This process involves shaking a homogenized sputum suspension with a hydrocarbon lighter than water (such as xylene or benzene). The mycobacteria, along with the hydrocarbon, float to the surface as foam, from which smears are prepared for bacterioscopy.

Fluorescence Cell/15.html">Microscopy also yields superior results; however, it requires a fluorescence microscope and expensive Dyes.

Anti-tuberculosis facilities widely utilize the culture method, which can detect MTB at concentrations as low as 20-100 per 1 ml of sputum and determine their sensitivity to anti-tuberculosis drugs. Lowenstein-Jensen and Finn-2 egg-based media are primarily used, with cultures grown in an incubator at 37 °С. The first growth of MTB colonies is typically observed only after 3 weeks, and sometimes as late as 2-3 months.

The biological method—inoculation into guinea pigs—yields positive results even when only a few mycobacteria are present in the material; however, it is expensive and rarely used.

A complete Blood count (CBC) serves as a supportive tool for tuberculosis Diagnosis. In Cytology/cytology/16.html">Early stages of tuberculosis, the hemogram may remain unchanged. Anemia develops only in disseminated and chronic forms. Tuberculosis is often accompanied by moderate leukocytosis (up to 15-10⁹/л), exceeding these levels only in cases of Caseous Pneumonia or Subacute Disseminated Pulmonary Tuberculosis. There is a moderate increase in the percentage of band neutrophils (a left shift in the formula), and lymphopenia develops. The ESR in tuberculosis typically ranges between 20-45 mm/h, and is higher in severe processes.

Urinalysis remains unchanged in uncomplicated pulmonary tuberculosis. In the presence of severe intoxication, mild proteinuria and occasional erythrocytes may be observed. A high leukocyte count in urine with an acidic reaction should raise suspicion of Renal tuberculosis. Persistent proteinuria and cylindruria may be signs of Renal Amyloidosis, which occasionally complicates chronic forms of tuberculosis.