What does ng/mL mean?
This measurement stands for nano-grams (of substance) per milli-Litre of volume (urine, oral fluid, blood, etc.) and is the unit generally used to describe the amount of substance in a sample. One nanogram is 0.000000001 of a gram, while a millilitre is one-thousandth of a litre; this is the equivalent to 1 gram in 1 million litres of water (an Olympic swimming pool contains 2.5 million litres of water).