Although there is a physical manifestation of what we call Lukemia, the fact that we conceptualize a range of symptoms and causes in a specific way is a social construct of sorts. We could conceptualize Lymphocytic and Myelogenous Lukemia as entirely different diseases, or we could choose not to conceptualize Lukemia as a special disease separated from other kinds of cancers at all.
Of course this is on a much lower abstraction that say money where the connection between the concept and our physical reality is very complex, but the way we conceptualize this set of physical states has a pretty massive impact on the way humans interact with each other.
Fundamentally, if we want to get really basic, the idea of healthy and unhealthy is even social constructed. A good example of this is American vs British dentistry. Americans make fun of British teeth for being ugly, but British people are apparently less likely to report pain or other negative effects associated with their dental health, and they tend to lose fewer teeth on average. The reason for this I see cited over and over is that Americans tend to associate dental health with cosmetics: bright, white, well straightened teeth, while the British tend to focus more on preventing tooth decay and loss.
It’s obviously more complicated than that but it’s a good example of how social constructs creep into a lot of the things we take for granted. The point of this isn’t necessarily to deconstruct the idea of Lukemia, which I chose as an unambiguously positive example of a social construct. Rather, I want to demonstrate that social constructs can be very powerful and aren’t some frilly nonsense that sociologists came up with to figure out how many angels can dance on the head of a pin.