Storage of Plasma in Primary Plasma Separator Tubes

When blood is centrifuged and the plasma stored in the primary tube, the concentration of an analyte in plasma depends on the rate of its metabolism and distribution between cellular and fluid compartments. Plasma separator tubes (PST) contain a gel which, on centrifugation of the sample, forms a barrier between cells and plasma and retards migration of analytes between these compartments. This allows the efficient use of primary tubes on analysers or the transfer of plasma to analyser cups without contamination by blood cells. Several drugs have been shown to adsorb to the gel, I and the gel may only be effective for a few hours in preventing migration of some analytes between plasma and cells.? Inadequate centrifugation could result in a layer of cells remaining on top of the gel, which could cause changes in the concentration of some plasma analytes on storage. We investigated the storage of plasma in primary PST, and compared different centrifugation times. We also evaluated whether addition of more gel to PST improved the stability of analytes in plasma.