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Impact of ultra-low temperature long-term storage on the preanalytical variability of twenty-one common biochemical analytes.

Author(s): Alegre E, Varo N, Fernández-Calle P, Calleja S, González Á

Publication: Clin Chem Lab Med, 2022, Vol. , Page

PubMed ID: 35470640 PubMed Review Paper? No

Purpose of Paper

Conclusion of Paper

Studies

1. Study Purpose

   This study compared levels of 21 biochemical analytes in serum before and after more than 5 years of storage at <-70°C. The authors also compared levels of eight biochemical analytes in fresh serum and serum that was stored for 7 days at <-70°C. Blood was collected in Vacutainer serum tubes with separator gel. After clotting for 30 min at room temperature, serum was separated by centrifugation at 2000 g for 10 min, aliquoted and stored frozen at <-70°C for longer than5 years (11 ±3.9 years). A total of 60 serum specimens were chosen based on initial analytical values for inclusion (diagnosis unspecified). Serum was thawed at room temperature and centrifuged at 2000 g for 10 min at 18°C. Levels of creatinine, potassium, sodium, urate, and urea were quantified on a Modular P analyzer. AST, ALT, calcium, CEA, cholesterol, CRP, direct bilirubin, Free T4, GGT, glucose, LDH, magnesium, PSA, total bilirubin, triglycerides, and TSH were quantified using the Cobas 8000 analyzer. Changes were considered relevant when the absolute value of the median percent deviation (PD) was greater than 0.5 times the coefficient of variance for the analyte (APS). To investigate if analytes were affected by the freeze-thaw process itself, five serum specimens were analyzed immediately after collection and again after 7 days at <-70°C.

   Summary of Findings:

   After frozen storage of serum for more than 5 years, significantly lower levels of ALT (P<0.001), cholesterol (P=0.002), creatinine (P<0.001), direct bilirubin (P<0.001), magnesium (P=0.011), urea (P=0.2), and urate (P<0.001) and higher levels of potassium (P=0.003), sodium (P<0.001), and triglycerides (P<0.001) were observed compared to pre-storage levels. Changes in ALT, creatinine, glucose, magnesium, potassium, sodium, total bilirubin and urate were analytically relevant based on a median percent deviation greater than 50% of the coefficient of variance (CV) for an analyte (the APS).  Importantly, reference change values also increased for analytes that were significantly affected by frozen storage longer than 5 y. In a small follow-up study (n=5), frozen storage of serum for 7 days did not significantly affect any of the analytes evaluated, but the percent deviation of potassium and ALT levels exceeded the APS. The following analytes were not significantly affected by storage at <-70°C for up to 5 years: AST, calcium, CEA, CRP, T4, GGT, glucose, LDH, PSA, total bilirubin and TSH.

   Biospecimens

   • Bodily Fluid - Serum

   Preservative Types

   • Frozen

   Diagnoses:

   • Not specified

   Platform:

   Analyte	Technology Platform
   Carbohydrate	Clinical chemistry/auto analyzer
   Electrolyte/Metal	Clinical chemistry/auto analyzer
   Glycoprotein	Clinical chemistry/auto analyzer
   Steroid	Clinical chemistry/auto analyzer
   Peptide	Clinical chemistry/auto analyzer
   Protein	Clinical chemistry/auto analyzer
   Small molecule	Clinical chemistry/auto analyzer
   Lipid	Clinical chemistry/auto analyzer

   Pre-analytical Factors:

   Classification	Pre-analytical Factor	Value(s)
   Storage	Storage duration	0 days 7 days 0 years >5 years
   Biospecimen Preservation	Type of fixation/preservation	Frozen None (fresh)
   Storage	Freeze/thaw cycling	0 cycles 5 cycles

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