Which specimen type is used for a single void bioassay?

• A. Urine
• B. Feces
• C. Nasal swab
• D. Blood

Answer: (A)

A single-void bioassay uses a urine sample. This is because many radionuclides are excreted through the kidneys into urine relatively quickly after intake, so a single urine sample collected from one urination provides a practical and sensitive indicator of recent internal contamination. Urine is easy to obtain, noninvasive, and its activity can be interpreted with known excretion patterns to estimate intake. Other specimen types are less suitable for a single-void approach: feces would require multiple samples over days due to slower and variable GI excretion; nasal swabs are not standard for internal dose assessment; blood reflects transient levels and often doesn’t capture the total excretion pattern needed for a reliable single-void estimate.