NAME IT A purified protein from Mycobacterium tuberculosis is injected into a person’s skin. A hardened, red area develops around the injection site within 3 days.

Video transcript

Hi, everyone and welcome back. Let's take a look at the next problem. It says tuberculin skin testing is commonly employed to identify mycobacterium tuberculosis infection. If the result comes out positive three days after the injection, what specific parameter is being measured through this test? A the skin redness of the injected area. B, the length of the in duration C, the level of pain or d the skin paleness of the injected area. So let's recall that in tuberculin skin testing, the person being tested has a subdermal injection of a purified protein derivative of the tuberculin protein. And when this small amount of fluid is injected right under the skin, it produces a little wheel like a raised welt on the skin at the site of injection. This is checked again in 72 hours or three days. As our question says, and if there is an increased area of hardness and swelling, that's a positive result, that's because this means there's an immune response to that protein. The body recognizes this tuberculin protein. It's already been exposed to tuberculosis or perhaps one's been infected by tuberculosis and that immune response is causing this hardness and swelling at the injection area. So when we look at our answer choices that corresponds to choice B the length of the in duration and duration there mean meaning a hardness and swelling. So you're looking for that, that swelling has still is still there after three days where as a negative result, any little wheel that formed from the injection will be gone. And then you measure the size of it in milliliters. And that's compared to a set standard for this tuberculin test. When we look at our other answer, choices, uh choice A the skin redness or choice D the skin paleness, the color of that in duration does not matter. It's li just looking at the size and then choice C the level of pain, this shouldn't be a painful uh effect at all. The injection itself might be painful but that swelling, you're not looking at a level of pain there. So the answer that we are looking for is the for the specific parameter being measured in a tuberculin skin test after 72 hours is choice B the length of the end duration. See you in the next video.