What are the diagnostic methods of tuberculosis?

1. Medical history, symptoms and signs

(1) Symptoms and signs: The symptoms of tuberculosis patients are generally not specific, but it is of great reference significance to clarify the development process of symptoms for the diagnosis of tuberculosis. The significance of signs in the diagnosis of pulmonary tuberculosis is limited.

(2) Diagnosis and treatment process: determine whether the patient is a newly discovered or a discovered case. Many patients with pulmonary tuberculosis are treated in general hospitals for the first time. The first diagnosis, especially the sputum excretion, drug variety, dosage and time, and adherence to regular medication should be recorded, which is of great value for determining the treatment plan in the future. If it is a recurrent patient, the treatment history is of reference significance for judging drug resistance.

(3) Contact history of tuberculosis: mainly family contact history, neighbors, colleagues, dormitories and other tuberculosis patients should also know. Record the patient's condition, bacterial excretion, treatment plan and medication law, contact time, contact closeness, etc.

2. Imaging diagnosis

Chest X-ray examination is an important method to diagnose pulmonary tuberculosis, which can find the early mild tuberculosis focus, determine the scope, location, shape, density, relationship with surrounding tissues and accompanying images of pathological shadows. Determine the nature of the lesion, whether there is activity, whether there is cavity, cavity size and cavity wall characteristics. The imaging characteristics of pulmonary tuberculosis are that the lesions mostly occur in the posterior segment of the upper lobe and the posterior segment of the lower lobe, with uneven density, clear edge and slow change, which is easy to form cavities and spread the lesions. The most commonly used photographic method for diagnosis is anteroposterior chest radiograph, which can often clearly show hidden lesions such as cardiac shadow, hilum, blood vessels and mediastinum, as well as lesions of middle lobe and lingual lobe.

CT can provide cross-sectional images, reduce overlapping images, easily find hidden lesions and reduce the missed diagnosis of minor lesions; Micro-miliary nodules were shown earlier than ordinary chest radiographs; Can clearly show the characteristics and properties of various types of pulmonary tuberculosis lesions, the relationship with bronchi, the presence or absence of cavities, as well as the deterioration of progress and the improvement of absorption; It can accurately show whether mediastinal lymph nodes are enlarged or not.

It is often used for the diagnosis of pulmonary tuberculosis and differential diagnosis with other chest diseases, and can also be used for guiding puncture, drainage and interventional therapy.

3. Detection of Mycobacterium tuberculosis in sputum

The main method of tuberculosis diagnosis is also the main basis for making chemotherapy plan and evaluating treatment effect. Every patient with suspicious symptoms of tuberculosis or abnormal shadows in the lungs must be checked for sputum.

(1) Sputum specimen collection: Sputum excretion of pulmonary tuberculosis patients is intermittent and uneven, and infectious patients may not find it once, so it is necessary to check the sputum several times. Bacterial positive patients 1 sputum sample is about 80% positive, 2 sputum samples are about 90% positive and 3 sputum samples are about 95% positive. Usually, newly diagnosed patients should send three sputum samples, including morning sputum and night sputum, that is, sputum. If there is no night sputum, it is advisable to leave a sputum sample 2 ~ 3 hours after morning sputum. Send two sputum samples to patients for follow-up at a time. Patients without sputum can obtain sputum samples through sputum induction technology.

(2) Sputum smear examination: a simple, rapid, easy and reliable method, but not sensitive.

When there are at least 5000 ~ 10000 bacteria in each milliliter of sputum, a positive result can be obtained. The usual method is Zygotsky-Nissl staining. Positive sputum smear can only show that there are acid-fast bacilli in sputum, and it is impossible to distinguish mycobacterium tuberculosis from non-mycobacterium tuberculosis. Because there are few nontuberculous mycobacteria, it is of great significance to detect acid-fast bacilli in sputum.

(3) Culture method: Mycobacterium tuberculosis culture provides accurate and reliable results for the examination of Mycobacterium tuberculosis in sputum, which is often used as the gold standard for tuberculosis diagnosis. At the same time, it also provides strains for drug sensitivity determination and strain identification. Mycobacterium tuberculosis takes a long time to culture, usually 2 ~ 6 weeks, and the positive results are reported at any time. After 8 weeks of culture, the unborn elderly reported negative results. Commonly used culture methods are modified Roche method and Nana Ogawa method. Recently, bacterial metabolites were determined by BACTEC TB460 or BACTEC MGIT 960 method, and the results can be obtained in about 2 weeks.

(4) Drug sensitivity test: It mainly provides the basis for the diagnosis of clinical drug-resistant cases, the formulation of reasonable chemotherapy schemes and epidemiological monitoring.

(5) Other detection techniques, such as polymerase chain reaction, nucleic acid probe detection of specific DNA fragments, chromatographic detection of specific components such as tuberculosis stearic acid and mycolic acid, and immunological detection of specific antigens and antibodies, have made some progress in the rapid diagnosis of tuberculosis, but these methods are still in the research stage and need to be improved and perfected.

4. Fibrobronchoscopy

Fiberoptic bronchoscopy is often used to diagnose bronchial tuberculosis and lymphadenitis. Bronchial tuberculosis is characterized by mucosal congestion, ulcer, erosion, tissue hyperplasia, scar formation and bronchial stenosis. Biopsy and Mycobacterium tuberculosis culture can be performed at the lesion. For pulmonary tuberculosis, secretions or lavage samples can be collected for pathogen examination, and samples can also be obtained through bronchopulmonary biopsy for examination.

5. Tuberculin test

It is widely used to detect the infection of Mycobacterium tuberculosis, but not tuberculosis. Tuberculin test has reference significance for the diagnosis of tuberculosis in children, adolescents and young people. Because BCG vaccination is widely carried out in many countries and regions, it is impossible to distinguish whether the positive tuberculin test is a natural infection of mycobacterium tuberculosis or an immune response to BCG vaccination. Therefore, the detection of mycobacterium tuberculosis infection by tuberculin test is greatly limited in areas where BCG vaccine is widely inoculated. At present, the World Health Organization and the International Union for the Prevention and Treatment of Tuberculosis and Pulmonary Diseases recommend the use of purified protein derivative (PPD)PPDRT23 to facilitate the comparison of international tuberculosis infection rates.

During the tuberculin test, 0. 1 ml (5IU) was injected intradermally into the middle and upper part of the left forearm, and the results were observed and recorded 48-72 hours after the test. Touch the edge of the induration with your finger, and measure the transverse and longitudinal diameters of the induration. The average diameter is = (transverse diameter+longitudinal diameter) /2 instead of measuring the flush diameter. Sclerosis is a specific allergic reaction, while flushing is a non-specific reaction.

The diameter of induration ≤ 4mm is negative, 5 ~ 9 mm is weakly positive, 10 ~ 19 mm is positive, ≥ 20 or < 20 mm but local blisters and lymphangitis are strongly positive. The stronger the reaction of tuberculin test, the more important it is for the diagnosis of tuberculosis, especially for infants. Generally speaking, children with negative reaction results indicate that they are not infected by mycobacterium tuberculosis, and tuberculosis can be ruled out. However, in some cases, tuberculosis cannot be completely ruled out, because the tuberculin test will be affected by many factors. It takes 4-8 weeks to establish a complete allergic reaction after tuberculosis infection, before which tuberculin test can be negative. Malnutrition, HIV infection, measles, chickenpox, cancer, serious bacterial infections, including severe tuberculosis, such as miliary tuberculosis and tuberculous meningitis. The results of tuberculin test are mostly negative and weakly positive.