Time-Dependent Stability of 22 Analytes in Lithium-Plasma Specimens Stored At Refrigerator Temperature For Up To 4 Days

Objective: To determine the maximum time-dependent stability of 22 analytes requested frequently for add-on testing in heparinized plasma samples stored at refrigerator temperature for up to 4 days and to compare the values for the maximum time-dependent stability (Tmax) of each analyte against previously published values. Methods: We quantified the plasma concentration of 22 chemistry analytes in patients’ plasma samples stored at refrigerator temperature for up to 24 hours (study 1, n = 40) or 4 days (study 2, n = 39). All analyte measurements were performed using the Siemens Dimension Vista 1500 chemistry analyzer. The maximum storage time over which an analyte was considered stable was defined as the latest time point at which 95.0% or greater of the delta values [the difference between the analyte value at time “n” ([A]tn) and time “0” ([A]t 0 , the initial analyte value)] for all specimens were within the allowable error limits (±E A) for each analyte. Results: The maximum amount of time that patients’ specimens spent at room temperature, which must be added to the amount of time spent at refrigerator temperature when discussing analyte stability, was approximately 3.5 hours. T max at refrigerator temperature for the 22 analytes we studied was less than 8 hours, TCK, CKMB, TNI, BUN, CREAT, TBILI, ALT, and AST; up to 8 hours, PHOS and DBILI; up to 16 hours, K and GLU; up to 24 hours, CO 2 ; up to 3 days, ALB; and up to 4 days, NA, CL, CA, MG, TP, ALP, AMY, LIP. Due to the extreme variability of the study designs used to determine values for T max reported in the literature, no meaningful comparison could be made between them and T max values from our study. Conclusions: Additional studies are needed, using our study design, to confirm the values for T max reported in the present study. In addition, there is a need for a standardized protocol or guideline for performing analyte stability studies that enables values for T max to be easily compared across published studies.