Estimating the long-term effects of storage at-70 degrees C on cholesterol, triglyceride, and HDL-cholesterol measurements in stored sera

We estimated the effects of long-term storage at -70 degrees C on serum tot al cholesterol, HDL-cholesterol, and triglycerides in specimens that had be en stored for up to 7 years. These estimates were made using measurements i n serial specimens collected from the placebo control group of the Air Forc e/Texas Coronary Atherosclerosis Prevention Study over a period of similar to 5 years. We compared the group means for pairs of serial specimens taken at 6- and 12-month intervals, assuming that (a) a negligible placebo effec t occurred between the serial specimen pairs; (b) in the absence of storage effects, the variation in the group means would reflect only normal biolog ical variation and would not materially affect the group means for the seri al specimens; (c) any systematic changes in these group means would reflect storage-related changes; and (d) storage-related changes are cumulative, i .e., the overall changes for a given storage period are the sum of the chan ges during previous storage periods. We observed average decreases of 2.0% per year for total cholesterol over 7 years and 2.8% per year in triglyceri des for the first 5 years. HDL-cholesterol decreased by 1.3% per year, but this change was not statistically significant. This approach may be useful for estimating storage-related changes for studies in specimens stored for a period of years and for which stability data may not be available. (C) 2000 American Association for Clinical Chemistry.