In my medical reports, how come the sum of HDL and LDL is not equal to the number of TOTAL cholesterol?

Question

In fact, the TOTAL cholesterol is always much greater than the sum of the two.

Answer 1

Most labs use the Friedewald formula which is an estimate rather than directly measuring LDL.

The formula is LDL = (total cholesterol level) - (high-density lipoprotein cholesterol [HDL] level) - (triglyceride level/5).

As you can see there is room for potential error. There are also other constituents that comprise total cholesterol, like VLDL (very low density lipoprotien). This accounts for why LDL plus HDL never adds up to Total cholesterol.

Good luck.