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Determination of high density lipoprotein-cholesterol in human plasma stored at -70 degrees C
Insights
Storing plasma samples at -70°C impacts high density lipoprotein (HDL)-cholesterol measurements. Pre-treating samples to remove other lipoproteins before storage minimizes these changes, improving accuracy for HDL-cholesterol analysis.
Area of Science:
- Clinical Chemistry
- Lipid Metabolism
- Biochemical Analysis
Background:
- Accurate measurement of plasma high density lipoprotein (HDL)-cholesterol is crucial for cardiovascular risk assessment.
- Long-term storage of biological samples can potentially alter analyte concentrations, affecting diagnostic reliability.
- Existing methods for HDL-cholesterol determination involve precipitation of other lipoproteins, which may be sensitive to storage conditions.
Purpose of the Study:
- To evaluate the impact of prolonged storage at -70°C on plasma high density lipoprotein (HDL)-cholesterol levels.
- To investigate whether the observed changes are dependent on initial HDL-cholesterol concentration.
- To compare the stability of HDL-cholesterol in unfractionated plasma versus heparin-MnCl2 supernatants after storage.
Main Methods:
- Plasma samples from 106 subjects were stored at -70°C for 1, 6, and 12 months.
- HDL-cholesterol was measured after treating plasma with heparin and MnCl2 to precipitate interfering lipoproteins.
- Changes in HDL-cholesterol levels were analyzed in relation to storage duration and initial concentration.
Main Results:
- Mean HDL-cholesterol decreased by 2.9% after 1 month and 5.1% after 12 months of storage.
- Storage-induced changes were dependent on initial HDL-cholesterol concentration, with lower levels tending to increase and higher levels to decrease.
- Storing heparin-MnCl2 supernatants, rather than whole plasma, resulted in a smaller mean decrease (3.3% after 12 months) that was independent of concentration.
Conclusions:
- Storage of unfractionated plasma at -70°C can lead to significant and variable errors in HDL-cholesterol determination.
- These errors are likely due to changes in the heparin-MnCl2 precipitability of lipoproteins during storage.
- Removing other lipoproteins prior to storage offers a more satisfactory method for preserving the accuracy of HDL-cholesterol measurements.
Abstract:
We determined the effect of storage at -70 degrees C on the determination of plasma high density lipoprotein (HDL)-cholesterol. Plasma from 106 subjects was stored for 1, 6, and 12 months, then treated with heparin and MnCl2 to remove other lipoproteins, and HDL-cholesterol was measured. The mean HDL-cholesterol level decreased by 2.9% after 1 month, and by 5.1% after 12 months. The magnitude and direction of the changes were not constant, but were correlated primarily with HDL-cholesterol concentration. After 1 month, samples with HDL-cholesterol levels below 40 mg/dl tended to increase, and those above this value tended to decrease. By 12 months, only those samples with HDL-cholesterol below 22 mg/dl tended to increase. Linear regression analysis indicated changes of 0.9-1.5 mg/dl for each 10 mg/dl initial HDL-cholesterol concentration. Storage of heparin-MnCl2 supernatants, rather than unfractionated plasma, minimized these changes. The mean HDL-cholesterol of stored heparin-MnCl2 supernatants was 3.3% lower after 12 months, and the change was constant regardless of lipoprotein concentration. The findings suggest the possible occurrence of changes in the heparin-MnCl2 precipitability of lipoproteins during storage, which produce errors in HDL-cholesterol analyses, and indicate that samples can be stored more satisfactorily if the other lipoproteins are removed first.