Small Agitated Blood Banks

Ticks are awesome, much like other creatures that survive through hematophagy (ie mosquitoes, leeches, vampires), these little bad boys secret an anticoagulant that keeps the platelets agitated and stops the process of hemostasis (blood clotting, that stops us from bleeding out). You bleed and they keep on dining.

So if we carry this to its rightful conclusion, vampires should secret a similar anti-coagulant. If so, that would be helpful in thinning the blood to prevent blood clotting.

That's what Buffy should have been doing on those years...hunting vampires and ticks...to extract their anti-coagulants!