Hello everyone,

For my study, I use plasma as well as PBMCs. I get heparinized blood sample from a local hospital usually within 2-3 hours of collection. I usually process the blood sample on the same day it is drawn.I centrifuge 15 mL blood it for 2000rpm for 12 minutes and collect the upper 2mL of plasma in fresh tubes. I mix by inversion the remaining blood and plasma and continue with Ficoll Paque standard procedure for PBMCs collection.

Today, I got a sample which was 24 hours or more old. I don't know the temperature at which it was stored. When I did the first step, centrifuged it at 2000rpm for 12 minutes, the plasma didn't separate. Tried repeating the same thing 2-3 times and the third time I used a different centrifuge thinking if something is wrong, but no separation. What could be wrong? I think the remaining sample won't have much viable PBMCs due to multiple centrifugation steps, so no point in going for Ficoll method further. And even if I get viable PBMCs, the overall procedure would be different for this sample, from all the other samples so I won't be using it for my studies.

Apart from sample being 24 hours old, nothing changed. What could be the reason for this strange outcome? Did anyone face any similar problem. My PI says, blood samples are okay for 2-3 days.