A simple procedure for the preparation of concentrated sera

We shall describe a simple technique to prepare concentrated sera that will have a near normal osmolality. A pool of sera is first frozen for 72 h at -20 degrees C and then allowed to thaw at 6 degrees C for 16 h. Care is taken to avoid any shaking of the bottle. The surface serum is then cautiously aspirated with a pipette. The left-over serum is mixed and filtered. To decrease the osmolality of this concentrated serum, we treated it with 200 mg of resin (Rexyn AG 501, H-OH) per 5 mL serum and then filtered it to eliminate the resin. We studied the effects of the height of the liquid column, the freezing temperature, the volume of serum decanted, the resin concentration and the duration of the extraction step. We also evaluated the stability of this concentrated serum at 6 degrees C, -20 degrees C and -70 degrees C. We also verified whether readjustment of the pH of the concentrated resin-treated serum would have improved its stability at -20 degrees C.