Dry ice exposure of plasma samples influences pH and lupus anticoagulant analysis.
Author(s): Odsæter IH, Lian IA, Bratberg K, Mikkelsen G
Publication: Clin Chem Lab Med, 2015, Vol. 53, Page 809-13
PubMed ID: 25257161 PubMed Review Paper? No
Purpose of Paper
The purpose of this paper was to determine the effects of dry ice storage and the temperature of subsequent frozen storage on plasma pH and results of the lupus anticoagulant test.
Conclusion of Paper
When plasma specimens were stored at -20°C, then incubated on dry ice for 24 h before being returned to -20ºC, median clot times for silica clotting time (SCT) and diluted Russel’s viper venom time (dRVVT) were longer, the ratio of dRVVT screening to confirmation results was higher, and median pH was lower compared to plasma specimens either stored at -20ºC for the entire 8 days or stored at -80ºC after incubation on dry ice. Importantly, changes in clot times resulted in false positives for lupus anticoagulant testing for 6 of 8 specimens tested.
Studies
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Study Purpose
The purpose of this study was to determine the effects of dry ice storage and the temperature of subsequent frozen storage on specimen pH and results of the lupus anticoagulant test. Plasma from 8 healthy patients was obtained by centrifugation of trisodium citrate blood, which was then transferred to 5 ml polypropylene tubes with skirted caps, centrifuged again, and aliquoted into fresh polypropylene tubes for storage. Specimens were then: 1) stored at -20ºC for 8 days; 2) stored at -20ºC for 3 days, then placed on dry ice for 24 h and returned to -20ºC for 4 days; or 3) stored at -20ºC for 3 days, then placed on dry ice for 24 h before being moved to -80ºC for 4 days. All plasma specimens were thawed in a 37ºC water bath before analysis.
Summary of Findings:
Compared to plasma specimens stored at -20ºC for the entire 8 days, specimens in which storage at -20ºC was interrupted by incubation on dry ice for 24 h had longer median clot times (for both SCT and dRVVT) in both screening and confirmation tests (p=0.008, all) and an increased ratio of dRVVT screening to confirmation test results (p=0.008) although the ratio of SCT screening to confirmation test results was unaffected. However, if plasma specimens were stored at -20°C followed by dry ice specimens then at -80ºC, SCT screening test results were significantly lower than when plasma was stored at -20ºC for the entire 8 days (0.90 versus 0.88, p=0.03). Importantly, after storage on dry ice followed by storage at -20ºC, 6 of 8 specimens were above the lupus anticoagulant diagnostic threshold, although none of the specimens were above the threshold when stored at -20ºC for the entire 8 days or when stored at -80ºC after storage on dry ice. Plasma pH was significantly lower when specimens were stored on dry ice then at -20ºC compared to those stored at -20°C (6.12 versus 7.32, p=0.001), although the decline did not occur when specimens were stored at -80ºC after incubated on dry ice.
Biospecimens
Preservative Types
- Frozen
Diagnoses:
- Normal
Platform:
Analyte Technology Platform Glycoprotein Hematology/ auto analyzer Morphology Hematology/ auto analyzer Small molecule Clinical chemistry/auto analyzer Pre-analytical Factors:
Classification Pre-analytical Factor Value(s) Storage Storage temperature -20ºC only
-20ºC and dry ice
-20ºC, dry ice and -80ºC