Stability Studies of Twenty-Four Analytes in Human Plasma and Serum

Abstract

Background: The stability and stoichiometric changes of analytes in plasma and serum after prolonged contact with blood cells in uncentrifuged Vacutainer® tubes were studied. Methods: We simultaneously investigated the stability of 24 analytes (a) after prolonged contact of plasma and serum with blood cells and (b) after immediate separation of plasma and serum (centrifuged twice at 2000g for 5 min). We verified biochemical mechanisms of observed analyte change by concomitant measurement of pH, Pco2, and Po2. Hemolysis was qualitatively and semiquantitatively assessed. All specimens were maintained at room temperature (25 °C) and analyzed in duplicate 0.5, 4, 8, 16, 24, 32, 40, 48, and 56 h after collection. Statistically significant changes from the 0.5 h mean were determined using repeated-measures ANOVA. The significant change limit was applied to determine clinically significant changes in measured analytes. Results: Fifteen of 24 analytes in plasma and serum maintained in contact with cells showed clinically relevant changes, with the degree of change more pronounced in most plasma specimens. All analytes in plasma and serum immediately separated from cells after collection were stable. Conclusion: Storage of uncentrifuged specimens beyond 24 h caused significant changes in most analytes investigated because of (a) glucose depletion and Na+,K+-ATPase pump failure; (b) the movement of water into cells, causing hemoconcentration; and (c) leakage of intracellular constituents and metabolites. Immediate separation of plasma or serum from cells provides optimal analyte stability at room temperature. When prolonged contact of plasma or serum with cells is unavoidable, use of serum is recommended because of the higher instability of plasma analytes.

Effect of sample handling and storage time on the stability of total CO2 in equine plasma

“…The linear decrease in plasma ctCO2 over time and the faster rate of decrease in plasma ctCO2 in the DC group most likely reflected prolonged contact time with leucocytes, erythrocytes and platelets. This result was consistent with those of 3 previous studies of human serum or plasma samples [9,10,12]. Storage of human serum or plasma samples in contact with blood cells at 25°C resulted in a significant decrease in ctCO2 after 56 h, with a faster rate of decline noted in plasma samples [12].…”

“…This result was consistent with those of 3 previous studies of human serum or plasma samples [9,10,12]. Storage of human serum or plasma samples in contact with blood cells at 25°C resulted in a significant decrease in ctCO2 after 56 h, with a faster rate of decline noted in plasma samples [12]. In addition, serum cHCO3 decreased by 4 mmol/l when human serum samples in contact with blood were stored for 24 h at 30, 32 and 37°C [9,10].…”

Stability of Routine Biochemical Analytes in Whole Blood and Plasma From Lithium Heparin Gel Tubes During 6‐hr Storage

“…We showed that CO 2 mean concentration decreases progressively in heparinized plasma, remaining stable up to 4 hr (mean bias -12.4%; ACL 15.4%), and then decreases significantly (mean bias -19.7% at +6 hr). Boyanton and Blick did not show any significant decrease in CO 2 in plasma up to 56 hr of storage at 25°C (greatest change -4.8%), neither did Oddoze et al up to 4 hr (-0.8%) (5,6). Nevertheless, in accordance with our result, Doumas et al also observed a growing decrease in plasma bicarbonate stored in capped original tubes (from -7% to -19% between +4 and +24 hr of storage) (10).…”

“…Stahl et al found negligible variations of stability in whole blood at 23°C for LDH (-3.3%, -5.5%, -1.3% at 2, 4, and 6 hr, respectively) and for K (-2.6%, -0.5%, -3.1% at 2, 4, and 6 hr, respectively) (12). Boyanton and Blick did not show any significant variation of stability for LDH and K after 4 and 8 hr, except a slight decrease in K concentration (-0.1 mmol/l) at 4 hr (6). Nonetheless, one must remember that stability of LDH and K depends on the temperature, which is known to influence enzymatic activities (13).…”

“…Such decrease had already been shown in previous studies, after 4-6 hr (-4.1% to -6.4%) at 20°C (12), after 2-4 hr (-4.4% to -7.9%) at 25°C (5), and after 10 hr (-11.2%) of storage at 21°C (2). Another study using ANOVA as significant differences showed that PHOS concentration decreased after 8 hr at 25°C due to glycolysis, or after 16 hr using significant change limit, then progressively increased after 32-56 hr of contact (6) due to hydrolysis of intraerythrocytic phosphate esters and leakage of the inorganic part (13). The decrease of PHOS in whole blood disappeared when tubes were stored at 4°C, at least up to 4 hr (5).…”