Loss of high density lipoprotein cholesterol in serum: effect of storage.

ABSTRACT

The objectives of the study were to determine the magnitude and pattern of loss of detectable high density lipoprotein cholesterol (HDL-C) as functions of time and temperature of storage. Serum from 29 consented adults were estimated for HDL-C (utilising polyethylene glycol and alpha-cyclodextrin) when freshly obtained and after storage at 4 degrees C, -20 degrees C and - 70 degrees C at varied intervals up to a maximum of 120 days. The concentration of fresh HDL-C ranged from 16.9 to 87.2 mg/dl. After 5 days of storing at 4 degrees C, an average of 5% of HDL-C could not be detected. After 120 days of storing at -20 degrees C, 6-8 mg/dl of HDL-C was 'lost, this represented 10-20% of the concentration of the fresh samples. Storage at -70 degrees C resulted in a 'loss' of 3%. The pattern of reduction of detectable HDL-C was such that the initial loss (first few days) was very rapid, reaching a nadir in 20 days. Examining individual serum samples, the loss ranged from minimal up to 30% of the original concentrations for all condition of storage. From further analysis of some portion of the data, there were suggestions that the concentration of triglyceride could be affect the loss of HDL-C with storage. Conclusion: Such rate of loss and heterogeneity of loss of detectable HDL-C, so far unexplained, may have implications in the management of epidemiological surveys involving storage of lipids in tropical countries.