(1) LDL is generally a calculated number. The formula used is not 
accurate when TG are under 100. You can see a better calculation here:

http://homepages.slingshot.co.nz/~geoff36/LDL_mg.htm

(2) LDL is composed of both high dense and low dense particles. The 
high dense are good and the low dense are bad.

Best would be to get a test that directly measures the LDL. It would 
also measure the high and low dense particles. I doubt any insurance 
will pay for it. It could cost a couple hundred dollars. And even 
with it the insurance company may not understand the difference in 
particle density.