Stability of human plasma catecholamines.

Human plasma catecholamines, measured by a radioenzymatic method, in general exhibit a marked stability when stored in plasma or whole blood. The storage of blood samples for several hours at room temperature, without prior separation of plasma, did not result in any losses of plasma noradrenaline or adrenaline. Moreover, the addition of thiol compounds (such as reduced glutathione, 2-mercaptoethanol or dithiothreitol) or other antioxidants (sodium metabisulphite) was not required during the storage. Although catecholamines were stable when kept in whole blood at room temperature, they were swiftly degraded when stored in buffer solutions in the absence of thiols. In one subject adrenaline and noradrenaline were repeatedly found to increase significantly in concentration in the course of the first 30 min of storage. The reason for this anomalous increase is unknown. The observed stability of catecholamines in blood is in striking contrast to some earlier reports. It appears to be premature to categorically neglect any precautions as regards the centrifugation, sampling and processing blood samples used for plasma catecholamine determinations; however, when a given routine method is employed one may check the apparent stability of noradrenaline and adrenaline. In some cases this may justify omitting some of the tedious and expensive arrangements suggested in the literature for sample processing.