Fingerprick cholesterol testing with the "Reflotron".

longer affected by any partial reversal of the binding equilibrium, which is a cause of assay “drift.” The length of time required for the completion of charcoal separation effectively limits the run sizes that can be accommodated with that procedure. The PEG separation requires the presence of the whole serum (or plasma) or the addition of normal gamma globulin to all tubes, to form a substantial pellet at the centriftigation stage. The method is limited to the use of analytes with a relative molecular mass of <1000 approximately, because larger molecules such as polypeptides may be partly precipitated by PEG solution at this concentration (150 g/L). However, the method is well suited to most of the analytes ordinarily labeled with tritium, such as steroids and nucleotides. As an example, we show in Table 1 a comparison of dehydroepiandrosterone sulfate (DHz.s) standard curves obtained by using either a standard charcoal separation protocol or the PEG method. For the PEG separation the RIA tubes (700-p.L incubation volume) were treated with 2.2 mL of a 200 g/L solution of PEG-6000 (BDH, Kilsyth Vic, Australia), which had been precooled to 4#{176}C, and 100 L of a 5 g/L solution of normal rabbit gamma globulin. The tubes were centrifuged (15 mm, 2400 x g, 4#{176}C) and the supernates were decanted and discarded. The pellets were redissolved with the addition of 1 mL of distilled water, allowed to stand for 30 mm at room temperature, vortex-mixed, and added to 10 mL of Aquassure liquid scintillation cocktail (Dupont-NEN, Sydney). Data obtained with the two separation methods produced virtually superimposable standard curves with similar performance characteristics.