Seven common mistakes when converting lab values
1. Using the factor of another test
Cholesterol and triglycerides need different factors (38.67 and 88.57) because their molar masses differ. Always use the factor of the test you are converting.
2. Confusing BUN and urea
Blood urea nitrogen (BUN, mg/dL) counts only the nitrogen. Urea in mg/dL is BUN × 2.14, and urea in mmol/L is BUN × 0.357.
3. Total, free or ionized
Calcium, testosterone, T3 and T4 exist as total and free values, and calcium and magnesium also as ionized values. The ranges differ; compare only the same measurement.
4. Scales with an offset
HbA1c in percent (NGSP) and in mmol/mol (IFCC) are linked by an equation with an offset: mmol/mol = (% − 2.15) × 10.929. A simple factor would be wrong.
5. Assay-specific units
D-dimer comes in FEU and DDU (roughly a factor of 2), and lipoprotein(a) in mg/dL and nmol/L (not convertible with a fixed factor). Check which unit the test really uses.
6. Mixing 24-hour and spot urine
A 24-hour amount (for example mmol/24 h) and a concentration in a spot urine sample (for example mmol/L) are different quantities and cannot be converted into each other.
7. Using another laboratory's reference range
Reference ranges depend on the method, age and sex. The range on your report belongs to the laboratory that measured. The ranges on MedConvert are general orientation values with a source.