Rules for Converting Vitamin D25 measurements

For those of us in USA, we use ng/ml, whereas the rest of the world uses nmol/l to measure Vitamin d25 blood levels. This makes it difficult to understand what researchers are using as cut-off points for "low" or "high" threshold values.
Here is the conversion formula:

• to convert nmol/L to ng/mL, multiply nmol/L by 0.4;

•  to convert ng/mL to nmol/L, multiply ng/mL by 2.5.]