What is an "equivocal" negative HTLV-III antibody test in blood donors?

@article{Barclay1986WhatIA,
  title={What is an "equivocal" negative HTLV-III antibody test in blood donors?},
  author={George Robin Barclay and W Hopcroft and D. Brian L. McClelland},
  journal={Lancet},
  year={1986},
  volume={1 8486},
  pages={912-3}
}