If radioactivity in the circulation from a previous nuclear medicine test is unaccounted for, results of plasma volume determination will be?

When radioactivity from a previous nuclear medicine test is present in the circulation and goes unaccounted for during the plasma volume determination, the results can be interpreted as falsely decreased. This occurs because the radioactivity can interfere with the measurement of the plasma volume.

In nuclear medicine, plasma volume determination typically involves administering a radiotracer and measuring its concentration in the plasma. If there is residual radioactivity from a prior test, it may contribute additional counts to the measurement, leading to the misinterpretation of the plasma volume as lower than it actually is, since the system is detecting signal contributions from both the current and previous tracers. Consequently, the presence of unaccounted radioactivity can mask the true plasma volume, resulting in a falsely low estimation.

In clinical practice, it is crucial to account for all radioactivity present in the circulation during measurements to ensure accuracy in determining physiological parameters such as plasma volume.