Stability Studies of Twenty-Four Analytes in Human Plasma and Serum (General Clinical Chemistry‪)‬

A general problem facing clinical laboratories is the integrity of uncentrifuged specimens for chemical analyses. Because prolonged contact of plasma or serum with cells is a common cause of spurious test results, plasma and serum should ideally be separated from cells as quickly as possible to prevent ongoing metabolism of cellular constituents as well as active and passive movement of analytes between the plasma or serum and cellular compartments. In the past, issues regarding serum analyte stability were a major concern because serum was the specimen preferred by most laboratories. However, some laboratories are switching to plasma because serum specimens have several inherent problems: (a) an increase in turnaround time because of the time necessary for clot formation, especially in patients receiving anticoagulant therapy; and (b) the risk of fibrin clot interference on automated analyzers, especially those with a common sample probe and no clot detection ability. However, although the changes that occur with analytes of uncentrifuged serum specimens are reasonably well investigated, no such data exist for uncentrifuged plasma specimens. Moreover, the changes in plasma analyte concentrations with and without prolonged contact with cells have yet to be simultaneously compared with those seen with serum analytes under identical conditions. Published literature pertaining to chemical analyte stability has addressed many issues related to serum specimens but largely neglected plasma. The stability of 72 analytes after prolonged contact of serum with cells has been described (1-7). The effects of prolonged storage on the stability of 31 analytes in plasma and serum separated from cells by a gel barrier are also known (6, 8-10). Lastly, the stability of 30 analytes in serum immediately separated from cells has been described (11-15), but no similar studies are available on plasma.