Serum bicarbonate stability study at room temperature- influence of time to centrifugation and air exposure on bicarbonate measurement reported according to the CRESS checklist.

Abstract

The aim was to evaluate the stability of serum bicarbonate at room temperature, depending on time to centrifugation and air exposure. Stability study was conducted in the laboratory of Clinical Hospital Centre Rijeka, Croatia in January-February 2022. Nine samples from 10 volunteers were collected in clot activator gel tubes (Greiner Bio-One). Bicarbonate was measured on Beckman Coulter AU480 (Beckman Coulter, Brea, USA). Three tubes were left at room temperature for30min, three tubes for 2h, three tubes for 4h until centrifugation. First tube from first group (baseline) wasmeasured immediately after centrifugation. Other measurements were expressed as percentage deviation (PD%) from baseline. First tube was remeasured after 1 and 2h (OT_0h_1h; OT_0h_2h). Second and third tubes were opened 1 and 2h after centrifugation (C_0h_1h; C_0h_2h). Second group of tubes was processed the same way with 2-hour centrifugation delay (WB_2h; OT_2h_1h; OT_2h_2h; C_2h_1h; C_2h_2h), and third group with 4-hour delay (WB_4h; OT_4h_1h; OT_4h_2h; C_4h_1h; C_4h_2h). PD%wascompared to Maximum Permissible Difference (MPD=5.69%). MedCalc statistical software was used (MedCalc, Ostend, Belgium). Bicarbonate baseline mean value (range) was 27.3 (23.4-29.6)mmol/L. Obtained PD% (95%CI) were: C_0h_1h 0.46 (-1.21, 2.12); C_0h_2h 0.18 (-2.22, 2.57); OT_0h_1h-6.46 (-7.57,-5.36); OT_0h_2h-10.67 (-12.13,-9.21); WB_2h-0.15 (-2.04, 1.74); C_2h_1h 0.01 (-1.52, 1.54); C_2h_2h-0.40 (-2.65, 1.85); OT_2h_1h-5.43 (-7.30,-3.55); OT_2h_2h-11.32 (-13.57,-9.07); WB_4h-0.85 (-3.28, 1.58); C_4h_1h-2.52 (-4.93, 0.11); C_4h_2h-3.02 (-5.62, 0.43); OT_4h_1h-7.34 (-9.64,-5.05); OT_4h_2h-11.85 (-14.38,-9.33). Serum bicarbonate is stable for 4h in closed uncentrifuged tubes, another 2h in closed tubes after centrifugation, and is unstable within 1h in opened tube.