Stability of chemical and immunochemical analytes in uncentrifuged plasma samples

Abstract

Background The stability of analyte concentrations in plasma after prolonged contact with blood cells in uncentrifuged lithium-heparin gel tubes was studied. Methods To investigate the stability of concentrations of 26 chemistry and 15 immunochemistry analytes, the simultaneously drawn samples ( n = 50) were measured after 6 h storage at +8°C and +22°C in whole blood and after immediate separation of plasma. The analyte concentrations were measured with a Roche Modular PPEE analyser using reagents from Roche Diagnostics. Results After prolonged contact with cells a clinically significant change was only observed for potassium where the mean value increased from 4.0 mmol/L to 4.8 mmol/L ( P < 0.001) when stored at +8°C. Conclusion Immediate separation of plasma from cells is recommended. However, when prolonged contact of plasma with cell is unavoidable, samples can be kept uncentrifuged for up to 6 h at +8°C or at +22°C. The stability of potassium, however, is temperature-dependent and cannot be measured from refrigerated blood samples.