Obtaining suitable results unaffected by pre- or postanalytical phases is pivotal for clinical chemistry service. We aimed comparison and stability of nine biochemical analytes after centrifugation using Barricor™ plasma tubes with mechanical separator
We collected samples on six healthy volunteers and nine patients from intensive care units into 6 mL plastic Vacutainer® lithium heparin tubes and 5.5 mL plastic Barricor™ plasma tubes. All tubes were centrifuged within 30 minutes after venipuncture. First, we compared results of nine biochemical analytes from lithium heparin tubes with Barricor™ tubes for each analyte using Passing-Bablok and Bland-Altman analyses. Second, we calculated the difference of analyte concentrations between baseline and time intervals in tubes stored at + 4 °C. Based on the total change limit we calculated the maximum allowable concentrations percentage change from baseline.
The majority of correlation coefficients were close to 0.99 indicating good correlation in the working range. Bland-Altman analyses showed an acceptable concordance for all analytes. In consequence, the Barricor™ tube might be an alternative to regular lithium heparin tube. Stability with this new generation tube is improved for eight analytes (except for aspartate aminotransferase) in comparison with regular lithium heparin tubes.
By using Barricor™ tubes and prompt centrifugation, supplemental analysis or re-analysis for eight analytes including alanine aminotransferase, alkaline phosphatase, C-reactive protein, high sensitivity troponin T, lactate dehydrogenase, NT-pro BNP, potassium and sodium could be performed within 72 h of specimen collection.
Many clinical laboratories for routine analytes have been using plasma or serum separator tubes for several years. The barrier gel allows rapid separation of serum or plasma from blood cells and reduces haemolysis. The gel used in these tubes is relatively inert, however several reports of gel affecting analyte concentrations have been published (
Becton, Dickinson and Company (BD) has recently developed the BD Barricor™ plasma blood collection tube, which has a mechanical separator, rather than a gel barrier. According to the manufacturer, the quality of plasma is improved, the centrifugation time is shorter (3 min
Six healthy volunteers (physicians) and nine patients from intensive care units (Lapeyronie Hospital, Montpellier) were included in the study group. Healthy volunteers as well as hospitalized patients were selected to cover both normal and pathological analyte levels. All the samples were obtained in the morning between 8 and 9 am after overnight fasting for healthy volunteers. The study was performed at Lapeyronie Hospital, Montpellier in June 2017, with appropriate ethics approval and with informed consent from all subjects. Two blood samples were drawn from each participant: one was collected into a 6 mL plastic BD Vacutainer® lithium heparin tube and the other into a 5.5 mL plastic BD Barricor™ plasma tube (Becton, Dickinson and Company, Franklin Lakes, NJ, USA). Both types of tubes were transported to the laboratory and centrifuged without automated pre-analytical system within 30 min after venipuncture at 20 °C in a dedicated Heraeus Multifuge X3 FR Centrifuge (Germany) according to the manufacturer’s recommendations (2000 x g for 10 min for lithium heparin tubes; 4000 x g for 3 min for Barricor™ plasma tubes). Thereafter, tubes were loaded on biochemistry analyser defining the time T0. Nine routine chemistry parameters were measured: alanine aminotransferase (ALT), alkaline phosphatase (ALP), aspartate aminotransferase (AST), C-reactive protein (CRP), high sensitivity troponin T (hs-cTnT), lactate dehydrogenase (LD), N-terminal pro brain natriuretic peptide (NT-pro BNP), potassium (K) and sodium (Na). All these biochemical analytes were quantified on a Cobas 8000© system including c701 and c502 module (for biochemical analytes) and e602 module (for immunoassays) from Roche Diagnostics (Meylan, France) using Roche reagent kits and calibrators. After the first analysis (T0), primary tubes were stored at + 4 °C according to our routine daily storage condition and re-analyzed at different time intervals (after 4, 24 and 72 h). The 72 h deadline was chosen because it corresponds to our daily practice. The visual appearance of the two types of tube at each analysis time was monitored.
First, Passing-Bablok regression analysis was used to compare results from lithium heparin tubes with Barricor™ tubes for each analyte. The slopes and the intercepts were considered non-significant when the 1 or 0 values fell within the 95% CI, respectively. Mann Whitney U-tests were used and the level of significance was set at P < 0.05. In addition, the scatter of differences was visualized by means of Bland-Altman plots and the calculated mean bias was reported for each analyte. Further, 95% confidence intervals (mean difference ± 1.96 SD) were reported to judge if biases are acceptable in medical practice. In addition, the bias was calculated for each analyte by the formula: [(average of Barricor results – average of standard lithium heparin results / average of standard lithium heparin results)] x 100. This percentage was compared with the desirable bias available from Ricos
For each storage time and for each analyte, the absolute difference of each sample (or percentage deviation) against the T0 concentration was calculated for the two types of tubes using the formula: [(Tx - T0Ref) / T0Ref] x 100. The mean percentage deviation (± SD) of the fifteen donors was calculated for the two types of tube. To assess the stability of analytes, we calculated total change limit (TCL) as described by Oddoze
7 - 65 | 1.00 |
0.00 |
21 |
21 |
0.20 |
- 0.7 | 11.5 | 0.933 | |
26 - 401 | 1.02 |
- 1.48 |
82 |
82 |
- 1.40 |
0.9 | 6.7 | 0.983 | |
12 - 50 | 1.03 |
- 1.5 |
20 |
21 |
0.20 |
- 1.3 | 6.5 | 0.819 | |
0.3 - 183 | 0.99 |
0.00 |
13.7 |
12.7 |
1.17 |
- 3.8 | 25.5 | 0.917 | |
3 - 159 | 0.99 |
0.00 |
11 |
11 |
0.61 |
- 0.8 | 23.7 | 0.932 | |
137 - 475 | 1.01 |
3.74 |
183 |
178 |
- 6.87 |
3.2 | 4.3 | 1.000 | |
30 - 8143 | 1.00 |
0.62 |
261 |
264 |
2.36 |
0.9 | 4.7 | 0.917 | |
3.4 - 4.9 | 1.00 |
0.00 |
4.0 |
4.0 |
0.02 |
- 0.5 | 1.8 | 0.630 | |
130 - 150 | 1.00 |
1.00 |
139 |
141 |
- 0.60 |
0.4 | 0.2 | 0.570 | |
ALT - alanine aminotransferase. AST - aspartate aminotransferase. CRP - C-reactive protein. LD - lactate dehydrogenase. ALP -alkaline phosphatase. hs-cTnT - high sensitivity troponin T. NT-proBNP - N-terminal prohormone of brain natriuretic peptide. K – potassium. Na – sodium. CI - confidence intervals. Values of biochemical analytes tested are given as median and interquartile range. P < 0.05 is considered statistically significant. *95% confidence intervals were calculated by the mean difference ± 1.96 SD. |
Bland-Altman difference plots for the nine biochemical analytes obtained with BD lithium heparin tubes and BD Barricor™ plasma tubes. The solid line shows the average of the differences obtained and corresponds to the bias between results obtained with two types of tubes. The dashed lines correspond to the lower and upper limits of the confidence interval at 95% (mean ± 1.96 SD) of the difference between results obtained with two types of tubes. ALT - alanine aminotransferase. AST - aspartate aminotransferase. CRP - C-reactive protein. LD - lactate dehydrogenase. ALP - alkaline phosphatase. hs-cTnT - high sensitivity troponin T. NT-proBNP - N-terminal prohormone of brain natriuretic peptide.
ALT, U/L | ± 21.75 | 6.02 (6.74) | 4.04 (9.86) | 1.40 (6.34) | 72 h |
ALP, U/L | ± 14.34 | - 0.47 (1.78) | - 0.86 (1.87) | - 1.13 (2.49) | 72 h |
AST, U/L | ± 10.83 | 7.45 (7.03) | 4.40 (8.27) | 11.96 (7.60) | 24 h |
CRP, mg/L | ± 38.72 | - 4.96 (12.46) | - 1.22 (12.70) | - 3.97 (12.70) | 72 h |
hs-TnT, ng/L | ± 9.37 | - 0.01 (5.15) | - 0.77 (2.45) | 5.78 (20.20) | 72 h |
LD, U/L | ± 8.82 | 7.84 (8.13) | 10.19 (11.06) | 15.98 (16.08) | 4 h |
NT-proBNP, ng/L | ± 18.35 | 0.52 (2.00) | 2.25 (3.10) | - 6.37 (7.28) | 72 h |
K, mmol/L | ± 6.21 | 0.51 (1.07) | 12.29 (7.12) | 53.39 (26.72) | 4 h |
Na, mmol/L | ± 3.64 | 0.72 (0.47) | 1.25 (0.88) | 0.34 (0.53) | 72 h |
ALT, U/L | ± 21.75 | 2.39 (8.57) | - 1.59 (7.97) | 1.98 (10.64) | 72 h |
ALP, U/L | ± 14.34 | - 1.42 (2.50) | - 0.93 (2.90) | - 1.74 (3.36) | 72 h |
AST, U/L | ± 10.83 | 4.36 (11.14) | 5.60 (11.05) | 12.37 (14.07) | 24 h |
CRP, mg/L | ± 38.72 | - 1.73 (2.96) | 2.14 (3.52) | - 0.49 (5.53) | 72 h |
hs-TnT, ng/L | ± 9.37 | 0.72 (9.03) | 2.27 (9.28) | 6.00 (17.13) | 72 h |
LD, U/L | ± 8.82 | 2.96 (3.96) | 4.67 (4.13) | 8.31 (10.22) | 72 h |
NT-proBNP, ng/L | ± 18.35 | - 0.78 (2.27) | 0.33 (3.22) | - 7.72 (7.32) | 72 h |
K, mmol/L | ± 6.21 | 1.16 (1.30) | 1.88 (1.18) | 4.90 (1.92) | 72 h |
Na, mmol/L | ± 3.64 | 0.00 (0.53) | 0.52 (0.50) | 1.00 (0.45) | 72 h |
ALT - alanine aminotransferase. AST - aspartate aminotransferase. CRP - C-reactive protein. LD - lactate dehydrogenase. ALP -alkaline phosphatase. hs-cTnT - high sensitivity troponin T. NT-proBNP - N-terminal prohormone of brain natriuretic peptide. K – potassium. Na – sodium. TCL - total change limit. SD – standard deviation. T4h, T24h, T72h – storage times in hours. Mean % differences are presented as mean (standard deviation). |
The correlation and the agreement in the working range of Barricor™ lithium heparin tube results with those of the regular lithium heparin tube were acceptable as seen by the regression and the Bland-Altman analysis with the majority of paired data within the agreement limits. However, Na concentrations in Barricor™ plasma tube tend to be higher than Na in regular lithium heparin tube. Since the analytical method is the same for both types of tubes, this might be explained with different acceleration during centrifugation process between kinds of tubes. The biological variation for sodium is very small (0.23%) and the calculated bias is close to the desirable bias (0.44%); for these reasons, we considered that the observed differences were not clinically relevant and results remained in normal range. Those data indicate that the use of Barricor™ tubes did not affect the concentrations of the nine analytes suggesting that Barricor™ tubes may be used interchangeably with regular lithium heparin tubes.
Further, we reported that concentrations for eight analytes remained stable up to 72 h in Barricor™ plasma tube, while AST activity increased significantly after 24 h whatever the type of tubes. Clearly, the Barricor™ plasma tubes improve post centrifugation stability in comparison with BD Vacutainer® lithium heparin, particularly for parameters sensible such as K and LD.
This study confirms the manufacturer’s claims concerning the visual quality of plasma, the shorter centrifugation time, which does not affect the concentrations of analytes, and the longer stability of analytes in samples stored post centrifugation in the primary Barricor™ lithium heparin tube. Therefore, supplemental analysis or re-analysis could be performed within 72 h of specimen collection for eight analytes (except AST) with Barricor™ lithium heparin tube samples.
The main limitation of our study is the number of samples available, but the recruitment of pathological subjects allowed the evaluation of values covering a large measurement range. The small number of samples evaluated could also explain the differences observed between the 2 types of tubes for the results of Na. In previous studies, results obtained from Barricor™ tubes were compared to plasma separator tube (PST) or serum with (SST) or without gel barrier (
In conclusion, at initial measure, the two different tube types are interchangeable for the nine analytes investigated on Roche platform. Our data demonstrated that the great advantage of these tubes is the stability of analytes after centrifugation during 72 h, allowing re-analyses or additional analyses if necessary for eight out of 9 measured analytes. Except for AST, analytes including ALT, ALP, CRP, hs-cTnT, LDH, NT-pro BNP, K and Na were unaffected when stored at + 4 °C for up 72 h after centrifugation.
We gratefully acknowledge the nurses and biochemistry laboratory personnel for technical assistance.
None declared.