In pre-employment drug testing, which specimen is quantified by weight rather than volume?

In pre-employment drug testing, which specimen is quantified by weight rather than volume?

• A. Hair sample
• B. Urine sample
• C. Blood sample
• D. Oral fluid sample

Answer: (A)

Hair testing uses the amount of drug per unit mass of hair, not per volume, because hair is a solid matrix whose moisture content and density vary. Labs weigh a predefined dried mass of hair and extract the drug from that known mass, then report the concentration as ng of drug per mg of hair. In contrast, fluids like urine, blood, and oral fluid are liquids with variable volumes, so their results are expressed per unit volume (e.g., ng/mL or μg/L). This weight-based approach standardizes measurements across samples and individuals, making hair a solid-matrix method.

Hair testing uses the amount of drug per unit mass of hair, not per volume, because hair is a solid matrix whose moisture content and density vary. Labs weigh a predefined dried mass of hair and extract the drug from that known mass, then report the concentration as ng of drug per mg of hair. In contrast, fluids like urine, blood, and oral fluid are liquids with variable volumes, so their results are expressed per unit volume (e.g., ng/mL or μg/L). This weight-based approach standardizes measurements across samples and individuals, making hair a solid-matrix method.