Stability of serum biochemical markers during standard long-term storage and with a single thawing

Aim. To study the effect of standard serum long-term storage at -70О C and with a single thawing on the biochemical markers by comparing the results of studies carried out in 2013-2014 and 2020.

Material and methods. The material was the blood serum of participants in the ESSE-RF study, which was stored in a specialized biobank from 2013-2014 at -70О C either continuously (n=149) or with a single thawing (n=20). Initially and in 2020, the quantitative determination of serum biochemical parameters was carried out using same equipment and standard techniques.

Results. Long-term storage at -70О C led to mild, but significant changes in almost all analyzed parameters: low density lipoprotein cholesterol (LDL-C) and apolipoprotein A1 levels decreased; levels of highdensity lipoprotein cholesterol (HDL-C), triglycerides, apolipoprotein B, glucose, and high-sensitivity C-reactive protein increased. Insulin and thyroid-stimulating hormone levels did not change during storage. The revealed strong positive relationships between the initial concentrations and those measured in 2020 in samples that were stored continuously indicate the relevance of such storage. In samples with single thawing, changes in most parameters were more pronounced.

Conclusion. The results of a prospective cohort study aimed at studying the stability of human serum samples during storage indicate the validity of long-term storage at -70О C without thawing. Freeze-thawing cycle of samples (even once) is unacceptable, since it leads to a pronounced LDL-C decrease. Given the fact that it is the LDL-C levels that is the target of lipid-lowering therapy, continuous low-temperature (not >-70О C) storage of blood serum samples is recommended.

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