I went to the lab for a blood test yesterday.  I have to do this regularly.  When my blood was being taken, it stop flowing into the vial and the person taking the blood test pulled out the needle.  Once she did that and looked at the vial, my blood lucked clumpy.  What could cause that?
Welcome to Chat Doctor. I am Chat Doctor. No need to worry because this is very common in lab. The vial content anti coagulant to prevent blood clotting. Sometimes it can be absent in vials because of manufacturer mistakes. Sometimes staff does not mix blood in vial because proper mixing is very important to prevent clotting. Thanx for query.