Blood lipid levels may exhibit mild seasonal variation with a drop in the summer and total cholesterol level peaking in the winter. The variation can be up to 5 mg/dL.

Serum total and HDL–cholesterol can be measured in fasting or non–fasting individuals. There are only small clinically insignificant differences in these values when measured in the fasting or non–fasting state.

The total cholesterol can vary by 4 to 11 percent within an individual due to multiple factors including stress, minor illness and posture. Values may also vary between different laboratories, with data suggesting that a single measurement of serum cholesterol can vary as much as 14 percent. Therefore in an individual with “true” serum cholesterol concentration of 200 mg/dL the range of expected values is 172 to 228 mg/dL.

More than one measurement of total cholesterol should therefore be obtained when treatment considerations demand a precise determination. Measurement of serum HDL–C and triglycerides may demonstrate even greater variability.

A standard serum lipid profile consists of total cholesterol, triglycerides, and HDL–cholesterol. Lipid profile should be performed after 12 to 14 hours of fasting to minimize the influence of postprandial hyperlipidemia. One can use either plasma or serum specimen. The serum cholesterol is approximately 3 percent lower than the plasma value.

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