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Letters to the Editor |
Institute of Clinical Chemistry, and Laboratory Medicine, Ernst Moritz Arndt University, Greifswald, Germany
aAddress correspondence to this author at: Matthias Nauck, University Hospital Greifswald, Institute of Clinical Chemistry and Laboratory Medicine, Ferdinand Sauerbruchstrasse, D-17487 Greifswald, Germany. Fax 49-3834-86-5502; e-mail matthias.nauck{at}uni-greifswald.de.
To the Editor:
Short in-laboratory turnaround time is important, and reducing centrifugation time can shorten this phase of the preanalytical process. The new BD Vacutainer® SSTTMII Advance (Becton Dickinson, article number 367955) has a semisolid, thyxotrophic acrylic gel with chemical composition identical to that of the previous SSTTMII tube. In the new Advance tube, however, the gel has been extended to 1 side of the tube, forming a gel nose with a larger initial contact surface that is supposed to accelerate gel movement during centrifugation to allow shorter centrifugation time (1). We compared gel barrier formation and hemolysis rates of the new Vacutainer SSTTMII Advance under a conventional centrifugation (CC) mode (13 min, 1700g; acceleration and braking time, 55 s) vs an accelerated centrifugation (AC) mode (5 min, 3000g; acceleration and braking time, 39 s) to determine whether this new Vacutainer system allows reduced centrifugation time while maintaining sample quality.
In vitro hemolysis can be caused by mechanical stress inflicted by higher g-forces, which might artificially increase several serum analytes and cause interference in some laboratory assays (2). Therefore we measured lactate dehydrogenase (LD), aspartate aminotransferase (ASAT), and potassium in paired serum samples as indicators of hemolysis, using a Dimension RxL Max (3). As a more sensitive and specific marker of hemolysis, free hemoglobin was measured immunologically on a Dade BN II system (all reagents and analyzers from Dade Behring). We used routine blood samples from inpatients and outpatients at the Greifswald University Hospital who had laboratory orders requiring 2 serum tubes. The university ethical board did not require approval by the human study committee for this study. Before centrifugation, samples were stored at room temperature for at least 30 min to allow complete coagulation. All centrifugation was performed in 1 centrifuge at 21 °C (Rotana 46 RSC Robot, rotor diameter 180 mm, 90 °C Hettich Zentrifugen), which is part of an automated preanalytical system (StreamLAB, Dade Behring). To avoid frequent changes in centrifugation settings, phase 1 (n = 104) and phase 2 (n = 104) of the study were performed in a crossover design. In phase 1, the 1st specimen of each pair was centrifuged within 60 min by the CC mode and the 2nd centrifuged in the AC mode within 120 min of arrival in the laboratory. In phase 2, the 2 centrifugation settings were reversed. All analyses were completed within 3 h.
In all tubes, the mean (SD) thickness of the gel layer was 10 (1) mm. No differences in gel integrity or wandering were noted in the tubes tested. Data from phases 1 and 2 are presented together because there were no marked differences in values from each phase (P >0.05) except for LD because of delayed centrifugation (P <0.001). Values for analytes from the paired tubes spun with the CC or AC mode were not significantly different (P >0.05 for all) (Fig. 1
). Passing and Bablock regression (4) showed AC = 1.00x + 0.00 for all (except LD where AC = 1.01x –4.09). We concluded that for these new tubes the AC mode did not increase the rate of hemolysis.
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Based on these results, we switched our routine centrifugation mode from CC (13 min) to AC (5 min) to decrease processing time by 8 min. To confirm that the AC mode did not increase hemolysis, we examined hemolysis (H)-indices before and after implementing the AC mode on a large number of samples. H-indices were determined photometrically at 405 and 700 nm (5). Retrospective examination of H-indices from 42 124 samples processed in the CC mode was compared with H-indices from 30 483 samples processed in the AC mode. The distributions of the different grades of hemolysis were identical for the 2 groups (see Table 1 in the Data Supplement that accompanies the online version of this Letter to the Editor at http://www.clinchem.org/content/vol53/issue4), with no increase in the frequency of hemolyzed samples during operation in the AC mode. We also investigated the frequency of clot occurrences before and after the introduction of the AC mode by examining the frequency of the error code "processing error" on the Dimension RxL Max, as a surrogate indicator for clot detection. The clot detection rate dropped from 0.09% to 0.05% (P <0.0001). Thus, the AC mode did not result in increased clot formation on the analyzers.
In conclusion, the BD Vacutainer SSTTMII Advance allows fast and reliable serum separation within 5 min at 3000g without change in sample quality regarding gel barrier formation, separation, and hemolysis. The AC settings can be recommended for routine use with the SSTTMII Advance tubes to shorten turnaround times.
Acknowledgments
We thank Becton Dickinson for providing sample tubes free of charge.
References
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