/Sci/ I need some help. I've been doing serum isolation these past two weeks. I keep getting red serum instead of the normal pale.

Typically I collect the blood from the trunk after excising the heart. However, I collect all the blood into one tube. I usually use my syringe 2-3 times when I do this. Can this issue be due to collecting the blood in the same tube? Or perhaps using the same syringe for the repeated collections?

I do let the blood sit for 30 minutes to let it clot then centrifuge at 4 degrees.