How to read the results of tuberculosis skin test

I believe that friends who have had intravenous infusions should know that if the doctor prescribes some medicines that are prone to cause allergies, a skin test is required before the patient uses it. If the skin test is normal, the injection can be given. If there is a problem, another medicine needs to be changed for treatment. As a relatively commonly used drug, Mycobacterium tuberculosis also requires a skin test before injection. So how do we interpret the results of a Mycobacterium tuberculosis skin test?

The reaction of the tuberculin test should be checked 48 to 72 hours later. If there is a red dot the size of a pinhole or slight redness and swelling at the injection site, and the diameter of the nodule is less than 0.5 cm, it is a negative reaction. If the diameter of the nodule at the injection site exceeds 0.5 cm but is less than 1.5 cm, it is a positive reaction. If the reaction at the injection site is strong or the diameter of the nodule exceeds 1.5 cm, it is a strong positive reaction. A positive reaction indicates that the body has an allergic reaction to Mycobacterium tuberculosis and has been infected with tuberculosis in the past, but it does not mean that you are sick, because people who have been vaccinated with BCG also have a positive reaction. A strong positive reaction indicates that there may be an active infection and further examination for tuberculosis should be performed. A negative reaction indicates no tuberculosis infection.

The traditional judgment criteria are: if the average diameter of the nodule is less than 5mm, it is negative; if it is greater than or equal to 5mm and less than 20mm, it is a positive reaction. [5-9 mm is weakly positive (+), 10-19 mm is positive (++)], and 20 mm or more (+++) or local blisters, necrosis, and lymphangitis are all strongly positive.

The "School Tuberculosis Prevention and Control Work Specifications" issued by the Ministry of Health and the Ministry of Education in 2010 stipulates that a strongly positive PPD test for students refers to an average nodule diameter ≥ 15mm or the presence of blisters.

Now that you know the answer to the question of how to read the results of a tuberculosis skin test, I would like to remind you that generally the nurse will do a tuberculosis skin test for you and will also tell you the results of the skin test. It doesn't matter if you can't understand it. However, you need to be reminded that if the doctor shows you tuberculosis but the nurse does not do a skin test, you need to pay special attention.