What are the diagnostic criteria for pulmonary tuberculosis?

Diagnosing pulmonary tuberculosis requires a comprehensive evaluation based on multiple indicators. The core criteria mainly include etiological testing, imaging examinations, clinical symptoms, tuberculin skin test, and interferon-gamma release assay. A detailed analysis is as follows:

1. Etiological examination: This is the key to definitive diagnosis and includes sputum smear microscopy and sputum culture. Sputum smear allows for microscopic observation of Mycobacterium tuberculosis in sputum samples—simple and rapid. Sputum culture can definitively identify the pathogen with higher sensitivity; a positive culture result confirms the diagnosis of pulmonary tuberculosis.

2. Imaging examination: Chest X-ray is a commonly used screening method that can detect tuberculous lesions in the lungs, showing characteristic findings such as patchy or linear shadows and cavities. Chest CT offers higher resolution, clearly revealing the location, extent, and details of lesions, thereby aiding early diagnosis and disease assessment.

3. Clinical symptoms: Common symptoms of pulmonary tuberculosis include persistent cough and sputum production lasting more than two weeks, possibly accompanied by hemoptysis (blood in sputum), low-grade fever, night sweats, fatigue, and weight loss. When these typical symptoms appear, tuberculosis should be highly suspected, and further diagnostic tests should be conducted accordingly.

4. Tuberculin skin test: Tuberculin is injected intradermally into the forearm, and the reaction is observed after 48–72 hours. A hard swelling (induration) with a diameter ≥5 mm at the injection site suggests possible infection with Mycobacterium tuberculosis. However, this test cannot differentiate between past infection and active disease, so results must be interpreted in conjunction with other diagnostic indicators.

5. Interferon-gamma release assay (IGRA): This test detects interferon-gamma released by the immune system in response to Mycobacterium tuberculosis-specific antigens, indicating whether infection has occurred. It has high specificity and helps distinguish true tuberculosis infection from immune responses caused by BCG vaccination, thus providing important diagnostic evidence.

Diagnosis of pulmonary tuberculosis should be based on a combination of multiple criteria to avoid misdiagnosis due to reliance on a single indicator. Once diagnosed, patients should promptly begin standardized treatment, adhere strictly to prescribed medication regimens, and take appropriate preventive measures to prevent disease transmission.