Any measurement taken has an inherent amount of inaccuracy to it. This uncertainty can be due to many things, ranging from human variables to the precision of the tools used to the measurement. Toxicology testing is the same, whether using immunoassays or mass spectrometry, every measure has some inaccuracy to it.
At Western Slope Laboratory, as an ISO 17025:2005 accredited forensic testing laboratory, we determined the uncertainty in every measurement produced for our clients. This uncertainty is quite inclusive taking into account the instruments and equipment that touch the samples as well as the efficiency of the aforementioned instruments and equipment. Simply put, when a value of a drug is reported by Western Slope Laboratory, we know specifically which drug is present and at what concentration.
For example, Methamphetamine in oral fluid run by UHPLC/MS/MS in our laboratory has a lower limit of quantification of 1ng/mL with an uncertainty of 5%. This means if we say there is 2 ng/mL of methamphetamine in a sample we are certain that methamphetamine is present in the oral fluid AND that the concentration is within the range of 1.9-2.1ng/mL
If you are a current client of Western Slope Laboratory and you have questions of what the uncertainty of a drug is please, contact our Director of Quality Assurance.