Some tests require serum or plasma (instead of whole blood) for the diagnostic.  If you do not have access to a centrifuge, one option is to use a battery-operated fan and connect your tubes of blood to the blades.

If you wish something more sustainable, you could build a hand-cranked centrifuge as designed by Dale Fritz and Pepper Jones at SIFAT (www.sifat.org).

Materials List (pdf here)        Directions for Construction  (pdf here)