Zeitschrift für molekulare Biomarker und Diagnose

Long Term Stability of Parameters of Lipid Metabolism in Frozen Human Serum: Triglycerides, Free Fatty Acids, Total-, HDL- and LDL-cholesterol, Apolipoprotein-A1 and B

Abstract

Eugène HJM Jansen, Piet K Beekhof and Erna Schenk

Background: In large epidemiological studies it is important to test the stability of biomarkers as a function of both temperature and duration of storage. In this study the stability of seven lipid parameters have been tested in human serum samples after storage at three different temperatures up to 1 year.

Methods: Serum samples of 16 human individuals were used in this study. The concentration of all parameters have been determined at T=0 and at several time points up to 1 year after storage at –20°C, –70°C and –196°C.

Results: Most of the lipid biomarkers, cholesterol, triglycerides HDL- and LDL cholesterol, apolipoprotein-A1 and –B are stable on long-term storage for one year at the three temperatures tested. The levels of both HDL- and LDL cholesterol showed a small decrease for samples stored at -20°C only. The free fatty acids, however, are not stable and showed a decrease to about 80% of the starting value. The rank order between the samples, however, remained very good.

Conclusions: This study shows that free fatty acids are not stable in human serum samples probably due to thawing and freezing effects, although the rank order and correlation between the samples from different time points remained the same. HDL- and LDL-cholesterol showed a very small deviation on storage at -20°C. The other lipid parameters remained perfectly stable in this study. No differences were observed between storage at -70°C or -196°C, Therefore it is advised to store serum samples at -70°C for longer periods.