The Collaborative International Dictionary of English v.0.48:

Buffy \Buff"y\, a. (Med.)
   Resembling, or characterized by, buff.
   [1913 Webster]

   Buffy coat, the coagulated plasma of blood when the red
      corpuscles have so settled out that the coagulum appears
      nearly colorless. This is common in diseased conditions
      where the corpuscles run together more rapidly and in
      denser masses than usual. --Huxley.
      [1913 Webster]