I had a test as part of a medical about 5 years ago. My level was quite high (can't remember the figure) which was a worry because my diet was, according to the Doc, quite good and 3 out of 4 grandparents died in their early 60s after strokes.
I modified my diet as much as I reasonably could, lost about 1kg in weight and had a retest. The overall level was still the same but the quantities of LDL and HDL had reversed themselves.
According to my GP, this was a very good thing because the level of the "bad"* cholesterol was more than compensated for by the level of the "good" one. IIRC, she divided one by the other.
*I can't remember which is which is which.