Wounds and cuts heal faster if there is no pressure on them and if they are kept relatively motionless. Movement disrupts the formation of the new blood vessels. Bandages keep the wound clean, keep harmful bacteria out, and maintain moisture to prevent your skin from drying out. Bandages should be changed daily.
You must wait at least eight weeks (56 days) between donations of whole blood and 16 weeks (112 days) between Power Red donations. Platelet apheresis donors may give every 7 days up to 24 times per year. Regulations are different for those giving blood for themselves (autologous donors).
The short answer to your question is simply that you do not need to wait until the blood test comes back before going ahead and donating blood. When you donate a unit of blood, the American Red Cross automatically performs a whole bunch of tests on the blood to make sure that the unit is safe and acceptable for use.