Preanalytical stability of zinc in whole blood serum and plasma tubes as measured by ICP-OES and colorimetry

AbstractBackground: Zinc deficiency is a global concern, particularly in low-income countries, but also among vulnerable groups in Western countries, such as children. Diagnosing mild or moderate zinc deficiency is however challenging because of non-specific symptoms and due to circulating zinc showingonly subtle changes, requiring high accuracy in measurement. Challenges to accurate measurement include variations from choice of analytical instrument, analysis performance, and preanalytical factors such as choice of sample matrices and delayed blood sample processing. This study aimed to examine the stability of zinc in plasma and serum, measured by the recommended inductively coupled plasma optical emission spectrometry (ICP-OES) method and a direct colorimetric assay on the fully automated Roche Cobas c702 analyzer. Methods: A total of 245 whole blood samples were stored at room temperature for 0-8 hours after blood sampling, then centrifuged for 10 minutes at 2000g (serum) or 5 minutes at 2650g (plasma), frozen at -20°C, and analysed respectively on ICP-OES and Cobas, the latter with the colorimetric kit from Sentinel diagnostics. Results: Serum zinc concentrations measured on Cobas and ICP-OES showed no statistically significant change up to 6 hours and never exceeded acceptable limits. Plasma zinc concentrations increased steadily over time, exceeding acceptable limits after 6 hours. There were statistically significant differences between zinc measurements on ICP-OES and Cobas in both serum and plasma. Conclusions: Zinc is stable for at least 8 hours in serum and up to 6 hours in plasma when measured by either Sentinel diagnostic colorimetric method on Cobas or ICP-OES.