Cholesterol and triglycerides: converting mg/dL to mmol/L

Cholesterol: factor 38.67

Total, LDL, HDL and non-HDL cholesterol share one factor because they are the same substance (molar mass 386.65 g/mol): mmol/L = mg/dL ÷ 38.67. Example: 200 mg/dL ÷ 38.67 = 5.17 mmol/L. In reverse: 5.0 mmol/L × 38.67 = 193 mg/dL.

Triglycerides: factor 88.57

Triglycerides are a mixture of fats; the usual convention is the molar mass of triolein (885.4 g/mol): mmol/L = mg/dL ÷ 88.57. Example: 150 mg/dL ÷ 88.57 = 1.69 mmol/L. The factor is therefore a convention and can differ slightly between laboratories.

Why not the same factor?

Cholesterol and triglycerides have very different molar masses. Using the cholesterol factor for triglycerides is off by more than a factor of two.

g/L instead of mg/dL

Some countries, for example France, report lipids in g/L: 1 g/L = 100 mg/dL. Apply the factor to mmol/L only after that step.

Calculated LDL

Many laboratories calculate LDL cholesterol from other values. The formula (for example Friedewald) depends on the unit used; the divisor is 5 for mg/dL and 2.2 for mmol/L. Do not mix the units.