Final answer:
A 'repeat-reactive' serological test result indicates that the donor's sample was initially reactive and remained reactive upon being retested in duplicate. The correct answer is option a.
Step-by-step explanation:
A serological test result that is noted to be "repeat-reactive" indicates that the donor sample was: a. Initially reactive, retested in duplicate, and both results were reactive. This outcome suggests that upon first testing, the sample showed a positive indication for the presence of antibodies or antigens of interest.
To confirm the initial finding, the sample was retested in duplicate, meaning two additional tests were conducted. Both of these subsequent tests yielded reactive results as well, which reinforces the likelihood that the detected antibodies or antigens are truly present in the donor's sample, and it is not a false positive.
In the context of serological testing, these steps are crucial to ensure the accuracy of the diagnosis and to rule out the possibility of false positives, particularly when testing for conditions such as infections or screenings prior to blood transfusions.