Stability of albumin, protein HC, immunoglobulin G, kappa- and lambda-chain immunoreactivity, orosomucoid and alpha 1-antitrypsin in urine stored at various conditions.
Urine samples from 10 randomly selected patients with advanced renal disease were each divided into six aliquots and a preservative solution containing benzamidinium chloride, EDTA, tris(hydroxymethyl)-aminomethane and azide was then added to three of the aliquots. Aliquots with and without additive were then stored at room temperature for up to 7 days, at 4 degrees C for up to 30 days and at -20 degrees C for up to 6 months. The concentrations of albumin, protein HC, IgG, orosomucoid and alpha 1-antitrypsin as well as the kappa- and lambda-chain immunoreactivities in the samples were determined by automated immunoturbidimetry or by single radial immunodiffusion after 1, 3, 7, 14, 30, 90 and 180 days of storage. All investigated proteins, except alpha 1-antitrypsin in native urine, were stable for 7 days in the samples stored at room temperature both in the presence and absence of additives. All investigated proteins, except alpha 1-antitrypsin in native urine, were stable for 30 days in the samples stored at 4 degrees C both in the presence and absence of additives. A more complex pattern was observed for the stability of the proteins in the frozen samples. The IgG level decreased rapidly in several samples stored without additives but not in samples stored with additives. The alpha 1-antitrypsin concentration decreased rapidly to about 50% of the initial value in several samples stored both with and without additives. The rate of the decrease for both the IgG and the alpha 1-antitrypsin level varied between samples and the main decrease for several samples was seemingly caused by the freezing and/or thawing per se and not by the storage period in between.