Minimum requirements for the estimation of measurement uncertainty: Recommendations of the joint Working group for uncertainty of measurement

Delayed sample processing can affect accurate glucose measurement. Our aim was to investigate the stability of glucose in samples collected in serum, sodium fluoride/potassium oxalate (NaF/KOx) and Glucomedics tubes processed according to different controlled pre-centrifugation delays (up to 180 min after venipuncture) in order to simulate prolonged sample transport between venipuncture and centrifugation. Samples were collected from healthy volunteers (n=80) into either serum or NaF/KOx and Glucomedics tubes. Glucose concentration was measured in samples centrifuged immediately after venipuncture and compared with tubes processed with a delay of 60, 120 and 180 min prior to centrifugation. Differences between baseline and respective delayed centrifugation glucose value for each tube type were tested using the paired t-test. Mean bias calculated for each tube type and delay protocol was compared to recommended quality specifications for glucose (2.2%). Glucose concentrations measured in all three delayed tube types were lower in comparison to respective baseline glucose concentrations measured in immediately processed tube (p<0.001). The highest decrease in glucose was observed in serum tubes in all specified time points (p<0.001), while glucose was most stable in Glucomedics tubes (p<0.001). The decrease in glucose observed for serum and NaF/KOx tubes was clinically significant at all specified time points while the bias for Glucomedics tubes did not exceed the criteria even with a centrifugation delay of 180 min. Glucose stability in un-centrifuged Glucomedics tubes is much superior to serum and NaF/KOx tubes. Glucomedics tubes can be left un-centrifuged for up to 3 h without affecting glucose concentration.

Background: Glucose measurements are crucial in diabetes diagnosis. We aimed to assess the effectiveness of liquid citrate acidification in preventing glycolysis and investigate glucose stability in serum, sodium fluoride (NaF/KOx) and Glucomedics tubes. Methods: Samples from 40 participants were collected in serum, lithium-heparin (LiH), sodium fluoride/potassium oxalate (NaF/KOx) and Glucomedics tubes. Glucose was measured within 60 min (baseline), 120 and 180 min from venipuncture. Serum, NaF/KOx and Glucomedics values at baseline were compared to LiH glucose concentration. Additionally, glucose values measured at 120 and 180 min from each tube were compared with the baseline value. Mean absolute bias for each tube and time point was calculated and compared to recommended criteria. The regression equation obtained comparing citrate to NaF/KOx tubes was used to recalculate glucose results retrieved from the laboratory information system. Results: Glucose measured in Glucomedics was higher (9.9%; p<0.001), while glucose in NaF/KOx and serum was lower compared to LiH (2.4%; p<0.001 and 3.2%; p<0.001, respectively). Biases for all tubes were clinically significant. Glucose remained unchanged at room temperature in all tubes for up to 180 min after venipuncture. Observed bias caused by Glucomedics leads to a 10.6% increase in diabetes prevalence (p<0.001). Conclusions: Inhibition of glycolysis is most effectively achieved using liquid citrate acidification, compared to LiH, NaF/KOx or serum. Due to clinically significant bias relative to reference glucose, the interchangeable use of different tube types for serial glucose measurements is not recommended. The replacement of NaF/KOx with Glucomedics tubes substantially impacts glucose results, giving marked rise in diabetes prevalence.

Introduction: We assessed the differences in faecal calprotectin (FC) concentrations measured by two assays depending on the stool consistency and extraction method. Materials and methods: Stool samples were extracted using the EliA Stool Extraction Kit, Calex® Cap extraction device and respective weighing methods, while FC concentrations were measured using the EliATM Calprotectin and Bühlmann fCAL® Turbo method and checked for within- and between-method variability with regard to extraction method and stool consistency category. Extraction yield was evaluated for impact of different sample incubation time (10 min and 1 h) in extraction buffer for both methods and for impact of different initial sample dilutions (1:50, 1:100, 1:500) for fCAL® Turbo method. Results: Results determined from Calex® Cap extracts were higher compared to weighing method extracts (mean bias 33.3%; P < 0.001), while no significant difference was found between results obtained with EliA Stool Extraction Kit and weighing method (mean bias 0.1%; P = 0.484), in both cases irrespective of stool consistency. Bühlmann fCAL® Turbo results were higher than EliATM Calprotectin results (mean bias 32.3%, P = 0.025 weighing method; and mean bias 53.9%, P < 0.001 extraction devices), the difference is dependent on stool consistency and FC concentration. Significantly higher FC extraction yield was obtained with longer sample incubation time for both methods (P = 0.019 EliATM Calprotectin; P < 0.001 fCAL® Turbo) and with increasing initial sample dilution for fCAL® Turbo method (P < 0.001). Conclusion: Preanalytical stool sample handling proved to be a crucial factor contributing to within- and between-FC assay variability. Standardization is urgently needed in order to assure comparable and reliable FC results.

Background: The aim of our study was to determine the difference between glucose concentration measured 30 min after venipuncture in ice-chilled heparin plasma sample and all currently available citrate buffer-containing tubes (Greiner Glucomedics, Greiner FC Mix and Sarstedt GlucoEXACT) and still widely used sodium fluoride/potassium oxalate (NaF/Kox) tubes from Greiner. Methods: Blood was collected from 20 healthy volunteers and 20 patients with diabetes into LiH, NaF/KOx, Glucomedics, FC mix and GlucoEXACT tubes. Glucose was measured within 30 min from blood sampling in duplicate on the Architect c8000 analyzer. Mean biases between all tube types were calculated and compared to the recommended criteria (1.95%). Additionally, glucose concentrations measured in all five tube types were compared using the Friedman test. Results: In the entire studied population, glucose concentrations measured in Glucomedics, FC mix and GlucoEXACT were higher (7.3%, 3.2% and 2.0%, respectively) than in the ice-chilled LiH tubes. When all glycolysis inhibitor-containing tubes were compared, Glucomedics tubes significantly differed from GlucoEXACT and FC mix tubes (biases −4.9% and 4.0%, respectively). In addition, there was a significant difference between the NaF/KOx tube and Glucomedics, as well as FC mix tubes (biases 7.1% and 3.0%, respectively). Conclusions: Glucose concentrations measured in recommended ice-chilled lithium heparin- and citrate buffer-containing tubes are not comparable. Significant biases exist between various glycolysis inhibitor-containing tubes; therefore, they cannot be used interchangeably.