You have probably already looked up the test, but here's a link that explains what an elevated LDH could possibly indicate. As you can see, there are many possible causes and even some false elevations, so perhaps it's just a fluke?
http://www.labtestsonline.org/understanding/analytes/ldh/test.html

I know that I am being very closely followed at MD Anderson and have labwork every 3 months, and they do not do an LDH test...