Harry's case is typical. For years, his doctor told him his LDL cholesterol of 123 mg was okay. But a heart scan score of 490 (90th percentile at age 52) made him question just where his coronary plaque came from.
Lipoprotein analysis told a very different story: His LDL particle number was 2400 nmol , meaning his trueLDL was more like 240 mg , nearly double the value of LDL obtained through his doctor. Harry had other sources of risk, too, but the LDL particle number was a clear stand-out.
Why does this happen? How can LDL cholesterol be so terribly inaccurate?
LDL cholesterols obtained in virtually all labs are not measured, they're calculated. The calculation was developed in the 1960s by Dr. Friedewald at the National Institutes of Health and therefore goes by his name (the Friedewald calculation). Dr. Friedewald derived this simple calculation to permit doctors across the U.S. to obtain LDL cholesterols, which were technically difficult to measure in those days by using measured HDL, total cholesterol and triglycerides.
Doctors were told that the only time that the Friedewald calculated LDL was inaccurate was when triglycerides exceeded 400 mg. So most family practitioners and internists still believe that calculated LDL's are, for the most part, quite accurate.
Nothing could be further from the truth. When LDL's are actually meaured, you find that LDL is rarely accurate. In fact, in our experience, inaccuracy of 30-50% is the rule, sometimes 100%. The one telltale hint that calculated LDL is wrong is when HDL is <50 mg--that's nearly everybody.
So what's your LDL? You won't really know unless it's measured. Our preferred method is NMR (LipoScience) LDL particle number, probably the most accurate of all. Second best: apoprotein B, direct measured LDL, and non-HDL. (We'll cover this issue much more extensively in an upcoming report on the www.healthcare.gov website in an extensive Special Report.)