A history of hypercholesterolemia influences cholesterol measurements.

Elevated plasma cholesterol levels identified during cholesterol screening are often lower when repeated because of the regression to the mean effect. We evaluated the effect of the presence or absence of a history of hypercholesterolemia on the regression to the mean phenomenon. Of 564 volunteers undergoing cholesterol screening, 53 subjects between the ages of 20 and 65 years found to have total plasma cholesterol levels above the 90th percentile for age and sex returned for a second determination. No dietary or behavioral changes occurred during the study. Individuals with a history of hypercholesterolemia showed no change in plasma cholesterol level between the first and second visits; however, a net 13.1% reduction in mean plasma cholesterol level was observed in the group without this history, with 59% of subjects dropping below the 90th percentile level. These findings demonstrate that the regression to the mean effect is confined to those individuals who do not report a history of hyperlipidemia. Subjects with this history are more likely to have their initial cholesterol elevation confirmed when the test is repeated.