I underwent a cholesterol screening yesterday, and they told me that my HDL (=‘good cholesterol’) was 68. My overall figure was 227 which they said was a little high. But they didn’t tell me my LDL value.
My simple question: Do I get the LDL value by subtracting the HDL value from the total? Or doesn’t it work like that?
No, the total-cholesterol does not equal the LDL-cholesterol plus the HDL-cholesterol.
In fact, total chol = LDL-chol + HDL-chol + VLDL-chol
In practice, direct measurement of VLDL-cholesterol is difficult
So, a close approximation (when triglyceride levels are less than about 400 or so) is used:
Total Chol = LDL-chol + HDL-chol + TG/5
The TG/5 figure is used to approximate this third major source of circulating cholesterol (VLDL-cholesterol) and assumes there’s a fixed molar ratio of TG/cholesterol in all VLDL for everyone. Clearly, not 100% accurate, but not too bad.
Sorry, in the above, I never explicitly defined TG to be trigylcerides.