They centrifuge your blood, keep the plasma, and return the red blood cells, yes. The centrifuge does not separate the PFAS, so it remains in the plasma when they take it.
The concentration of PFAS in the plasma remains similar to the concentration in your remaining blood; as your body replaces the plasma, the concentration falls.
Don’t they put the blood back in you after taking the plasma out of it?
They centrifuge your blood, keep the plasma, and return the red blood cells, yes. The centrifuge does not separate the PFAS, so it remains in the plasma when they take it.
The concentration of PFAS in the plasma remains similar to the concentration in your remaining blood; as your body replaces the plasma, the concentration falls.