Jim:
In a previous career I used to do blood work with a microscope. The most common error even among lab tech’s with experience is false rouleaux, that is, clumping caused by manhandling the blood, mistaken as true rouleaux. Even squeezing the finger to get a drop of blood can cause this. Putting the slide on the blood too hard can do this. Washing with saline if not perfect in osmolarity will cause other artifacts. While I am in full agreement with the McGyver school of expediency, the previously mentioned idea IMHO, is not something that can be done by the untrained and given the lethality of a mistake, not worth it. At $6 a card for [Eldon] blood type cards, just get the cards. If you have a patient who is low on blood and don’t have anti-shock pants and need to buy some time, consider tightly wrapping the limbs with whatever is handy. Towels, blankets, Ace bandages. This will force the remaining blood to the vital organs and brain.- SF in Hawaii