In the U.S. values for serum cholesterol, LDL-cholesterol, and other serum lipids are reported as milligrams per deciliter, e.g., 200 mg/dL. The rest of the world uses SI units (Systeme International d'Unites). This system presents hematological and clinical chemistry values in molar concentrations per liter. The SI is the standard international measurement system, and for at least a decade most research and medical journals have required that results be reported in SI units. Patients in the UK and Europe know their personal serum lipid values in SI units. In the U.S. the medical community has continued to use the old, familiar mg/dL values in patient care and practice.
However, SI units make more biological sense and that is why they have become the international standard. Molar concentration, not weight, is the basis for the SI units. Molar concentration refers to numbers of molecules, for example the number of cholesterol molecules in blood. Biological reactions occur on a molecular basis, and molar concentrations reflect the proportional amounts of various components within the body that are available to participate in reactions. Milligram or gram amounts are based on the weight of a substance present in the body. Large molecules that are heavy may appear to be present in larger amounts than small, light-weight molecules. Yet, in reality there may be very few of the heavy molecules and vast numbers of the lightweight molecules. It is the actual number of molecules of a substance that determines the potential for action in the body.
If you come across SI units in your reading, here are the conversion factors for lipids and some examples to help you translate them into the U.S. values.
Example: Total serum cholesterol 5.20 mmol/L (millimole per liter) = 200 mg/dL 250 mg/dL = 6.46 mmol/L Conversion factor 0.02586 To convert mmol/L to mg/dL: divide mmol/L by conversion factor To convert mg/dL to mmol/L: multiply mg/dL by conversion factor
Example: LDL-cholesterol 3.36 mmol/L = 130 mg/dL Conversion factor 0.02586
Example: HDL-cholesterol 0.9 mmol/L = 35 mg/dL Conversion factor 0.02586
Example: Serum triglycerides (TG) 1.80 mmol/L = 160 mg/dL Conversion factor 0.01129
The tragedy of science is the slaying of a beautiful hypothesis by an ugly fact. T H Huxley