The skin test for tuberculosis generally has four results: negative, weakly positive, positive, and strongly positive. The observation method is to check the condition of the injected skin 48 to 72 hours after the injection of the pure protein derivative of tuberculin.
1. Negative: no reaction or slight reddening of the skin, the diameter of the nodule is less than 5mm. negative result does not mean that there is no infection of tuberculosis bacillus, and there is a possibility of false-negative result (e.g., within 4-8 weeks of infection of tuberculosis bacillus, the immune response has not yet been established, and the result at this time may be negative, or people using glucocorticosteroids, immunosuppressants may also show negative results, etc.).
2. Weakly positive: the diameter of the nodule is within the range of 5mm to 9mm. This indicates possible exposure to Mycobacterium tuberculosis or previous infection or BCG vaccination. Combined with sputum smear, sputum culture, chest CT, tuberculosis antibody test, if the test results support the diagnosis of tuberculosis, anti-tuberculosis treatment is needed.
3. Positive: The diameter of hard nodules is within the range of 10mm to 19mm. A positive reaction does not necessarily mean that the patient has tuberculosis, and there is a possibility of false-positive results (e.g., atypical mycobacterial infection, ultraviolet light irradiation, injection of BCG vaccine, etc.).
4. Strong positive: the diameter of hard nodule is more than 20mm, and blisters and necrosis may appear on the skin. It suggests that the patient may have active tuberculosis.
Tuberculosis is an infectious disease of the respiratory system, but not every patient with tuberculosis is infectious, and only patients with bacilli excreted in sputum are infectious, mainly through respiratory transmission.
Tuberculosis skin test results are not sufficient to diagnose tuberculosis, the diagnosis also needs to go to the hospital as soon as possible to improve other related examinations, comprehensive diagnosis.