The invention provides methods for producing therapeutically active proteins in a blood sample, the method comprising incubating a blood sample in a blood collection or storage device containing one or more substrates, the one or more substrates (a) having a density less than that of erythrocytes and greater than that of plasma and being capable of floating in the blood sample, (b) comprising silicates material or (c) comprising material capable of adhesion to one or more blood cells.
