查了一下关于卡介苗和TB皮试阳性的关系，发现有三种说法

我做以前做TB皮试的时候也是阳性，而且反应面积很大，当时大夫说应该不是卡介苗的原因，而是曾经接触过感染源。当时我就觉得有些疑问，不过也没多想。今天看到有人提起，去网上查了一下，发现有三种不完全相同的说法。而且这三种说法都来自政府官方网站。

1。Skin test reactivity to a good BCG vaccination is generally less than to true tuberculosis infection, and it wanes faster over the years. Reactivity in adults due to BCG given in infancy is often less than 10 mm. （source：www.mass.gov）

这和我当时看的大夫说法相同，称多年前注射的卡介苗一般不会引起很大的皮试反应面积。

2。The size of a TB skin test reaction in a BCG-vaccinated person is not a factor in determining whether the reaction is caused by latent TB infection (LTBI) or the prior BCG vaccination. (source：www.cdc.gov )

这和第一种说法不同，称皮试反应面积不能区别卡介苗和隐性TB感染。

3。BCG can cause a positive skin test, especially if the vaccine was given after early infancy, if it was given several times, and if it was given within the last five to ten years. Nevertheless, since many persons who have immigrated to the U.S. are at risk of TB even though they received BCG, the recommendation in the United States is to interpret skin tests and recommend treatment regardless of whether you have had BCG. In other words, if you have a positive skin test and are from a part of the world where TB is common, you should assume that it is due to TB exposure and implies a risk of future disease and not that it's positive because of the BCG. Nevertheless, you should let your doctor know if you had a BCG, when and if you had it more than once. （source: www.kingcounty.gov )

大意是说，卡介苗也许会引起TB皮试的阳性反应，但因为打卡介苗的移民多是来自TB高发区，所以治疗标准还是应该以皮试结果为准。

所以，感觉在美国这方面也没有特别明确的说法。如果我有理解不准确的地方欢迎大家纠正。