Effect of storage at 4 degrees C and -20 degrees C on lipid, lipoprotein, and apolipoprotein concentrations

We have investigated the effects on lipid, apolipoprotein, and lipoprotein measurements of storing unfractionated serum at 4 degrees C for 10 days and at -20 degrees C for 10 days or 3 months. Total serum concentrations of lipids were stable, although apolipoprotein B showed a 5.3% increase after 3 months at -20 degrees C (P < 0.001). Increases in low-density (LDL) and high-density lipoprotein (HDL) triglyceride and very-low-density lipoprotein (VLDL) esterified cholesterol concentrations and decreases in free cholesterol concentrations in LDL and HDL after storage of serum for 10 days at 4 degrees C were verified by fractionation of lipoproteins by sequential flotation ultracentrifugation. Ten days' storage of serum at -20 degrees C resulted in increases in VLDL triglyceride and phospholipid concentrations, with decreases in HDL concentrations in triglycerides and phospholipids; changes were more extensive after 3 months at -20 degrees C. We conclude that ultracentrifugation of serum for lipoprotein analysis should be performed as soon as possible after collection.