LDHLactate dehydrogenase
An enzyme present in almost every tissue, so it flags damage without saying where.
Lactate dehydrogenase is an enzyme involved in turning glucose into energy, and it is present in nearly every cell in the body. When cells are damaged it spills into the blood.
It matters as a general, deliberately non-specific marker of cell turnover or damage. Because it comes from everywhere, a raised LDH says something is happening without saying where, which is both its use and its limitation.
In practice it is easily raised by a difficult blood draw, since red cells damaged in the tube release it. It is interpreted alongside more specific markers rather than acted on alone.