culture cells and human plasma

[Harald Heider]

I am trying to add human plasma (derived from citrate blood) to cell 
cultures. The set-up is the following: HEK293 cells are cultured in 12 
well-plates in 1 ml of complete medium (DMEM with serum and 
antibiotics). Then 700 microliters of human plasma are added (without 
removing the medium). After 4h the whole stuff is coagulated! It is not 
the medium and not the incubation period (I tried this). Does anybody 
know how to avoid the clotting under these circumstances?

Thanks a lot

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