Critically low sodium levels due to concentration gradients formed in patient samples after undergoing a freeze-thaw cycle.
Author(s): Marquez CP, Petersen JR, Okorodudu AO
Publication: Clin Chim Acta, 2018, Vol. 484, Page 218-222
PubMed ID: 29807019 PubMed Review Paper? No
Purpose of Paper
This paper investigated the effects of sampling position within the serum layer, a single freeze-thaw cycle, post-thaw storage duration, and post-thaw mixing on the concentration of clinical chemistry analytes in serum separator tubes (SSTs).
Conclusion of Paper
The average concentration ratio (CR) for all analytes was higher in the serum obtained from just above the separator and lower in the serum from the top of the tube than in the serum obtained immediately after inversion. When specimens were freeze-thaw cycled once after storage at either temperature and thawed for 1 h or 3 h, the average concentration of most analytes was approximately 50% and 60% that in the specimen before freezing. When mixed after thaw and before analysis, the CR increased to slightly above baseline, which the authors attribute to the removal of the more dilute areas to complete the analysis at 1 and 3 h post-thaw.
Studies
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Study Purpose
This study investigated if concentration gradients exist within serum with low sodium concentrations. From each of three specimens in SSTs (collection and processing details not provided), 200 µL aliquots were removed from the top and bottom layer and analyzed. The tubes were then inverted six or more times and analyzed. Levels of sodium, chloride, potassium, blood urea nitrogen, creatinine, calcium, and glucose were determined in the aliquots as well as in the original tube after mixing using a Vitros 5600.
Summary of Findings:
Concentration gradients were observed for all analytes, with the highest concentrations occurring just above the separator. The authors report that the CR for each analyte was comparable to the other analytes tested for each specimen and thus the CR averages presented are for all analytes from each specimen. The average CR in the top of the tube to that in the mixed specimen ranged from 0.62-0.82, depending on the patient, and the CR of analytes from the bottom of the tube was 1.11-1.46.
Biospecimens
Preservative Types
- None (Fresh)
Diagnoses:
- Not specified
Platform:
Analyte Technology Platform Carbohydrate Clinical chemistry/auto analyzer Small molecule Clinical chemistry/auto analyzer Electrolyte/Metal Clinical chemistry/auto analyzer Pre-analytical Factors:
Classification Pre-analytical Factor Value(s) Biospecimen Aliquots and Components Biospecimen heterogeneity Sampling at multiple levels
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Study Purpose
This study investigated the effect of freeze-thawing specimens after storage at -20˚C and -70˚C, thaw duration, and post-thaw mixing on levels of ten clinical chemistry analytes. Six expired patient specimens in SST were analyzed and then three were placed at -20˚C and three at -70˚C. Specimens were then thawed at room temperature and analyzed after 1 h and 3 h. After the 3 h analysis, specimens were mixed by inversion six times and reanalyzed. Total bilirubin, calcium, total protein, albumin, alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), cholesterol, triglycerides, and high density lipoprotein (HDL) were determined on a Vitros 5600. Concentration ratios (CR) for each analyte were determined but only the average CR for each condition was presented.
Summary of Findings:
The bilirubin levels were very low, resulting in large fluctuations, and ALT appeared to be less affected by freeze-thaw, thus both were excluded from analysis. The average CR of the other analytes was just over 50% of baseline 1 h after thawing when stored at -20˚C (0.52) and -70˚C (0.57). When thaw was extended to 3 h, the average CR of the analytes was 0.63 for the specimens frozen at -20˚C and 0.64 for that frozen at-70˚C; however, when mixed after thaw and before analysis, the CR increased to slightly above baseline (1.07 for -20˚C and 1.06 for -70˚C), which the authors attribute to the removal of the more dilute areas to complete the analysis at 1 and 3 h post-thaw.
Biospecimens
Preservative Types
- None (Fresh)
- Frozen
Diagnoses:
- Not specified
Platform:
Analyte Technology Platform Carbohydrate Clinical chemistry/auto analyzer Electrolyte/Metal Clinical chemistry/auto analyzer Steroid Clinical chemistry/auto analyzer Lipid Clinical chemistry/auto analyzer Small molecule Clinical chemistry/auto analyzer Pre-analytical Factors:
Classification Pre-analytical Factor Value(s) Storage Freeze/thaw cycling 0 cycles
1 cycle
Analyte Extraction and Purification Sample mixing Not inverted
Inverted 6 times
Storage Storage temperature -20˚C
-70˚C
Storage Post-thaw duration 1 h
3 h