Expert: Todd Bublitz, RCEP - 9/1/2008

Question
With regard to a full lipid cholesterol test, if I took the test right after eating would my LDL be higher or lower than if I fasted for twelve hours; would my HDL be higher or lower than if I fasted for twelve hours. Thank you very much for your response. Al Brown

Answer
Al,

As you probably know, some of our lipid levels change dramatically after eating (or drinking anything with calories).  The most effect is on the triglyceride level which can increase a very significant amount.  A significant increase in triglyceride levels can cause a drop in the HDL level.  Therefore, having a lipid test soon after eating can cause the HDL to be lower.

The actual level of LDL should not change significantly after eating.  However, most labs use a calculation to estimate LDL levels.  The formula is:
LDL=Total Cholesterol-(HDL+Triglycerides/5).  
If you plug in "normal" values into this formula, you get the following:
LDL=200-(40+150/5)
LDL=130

If you plug in high triglycerides and low HDL you get the following:
LDL=200-(35+300/5)
LDL=105

As you can see, eating right before a lipid test can give you a false low LDL level.

Your doctor can ask the lab to do a "direct LDL" level - where the lab actually counts the LDL particles.  If this were done, the LDL level would be accurate whether you've eaten or not.

I hope this answers your questions.

Todd