For confirming bioassay results, when should the follow-up sample be taken?

• A. 2 weeks post exposure
• B. 3 days post exposure
• C. Immediately after exposure
• D. 1 week post exposure

Answer: (D)

Timing a follow-up bioassay is about watching the body's excretion pattern after a potential intake. An immediate sample often reflects surface contamination rather than true internal uptake, so it isn’t reliable for confirming uptake. Waiting about one week after exposure usually falls in a window where the radionuclide, if taken in, has begun to be excreted and can be measured reliably for confirmation and dose assessment. If you wait only a few days, the excretion signal may not yet be detectable for many radionuclides; waiting two weeks can let levels drop and become harder to confirm. In short, one week provides a practical balance to demonstrate an internal burden and estimate dose without losing the signal to natural clearance.