An attempt was made to correct variations in the measurement of total cholesterol levels in order to study year-by-year trends in the values of total cholesterol measured at our center as part of the mass health screening project.
The sutudy covered the period from 1979 to 1996.
In coming to grips with variations in the measurement, we used the month-specific means of in-house pooled serum, which is internal quality control serum. On the basis of. the in-house pooled serum, the use of which began in June 1993, we observed variations, while correcting variations between lots and computing the values of in-house pooled serum on one and the same level. Variations in the means of total cholesterol in the mass health screenings proved similar to those in the levels of measurement, suggesting that distortions in the measurement could be corrected. To compensate for the distortions, we computed conversion factors so that the vallues of the in-house pooled serum observed at one and the same level could be compatible with the levels of secondary certified reference material for the measurement of serum lipids and then used the factors to correct the age-specific means of total cholesterol recoreded in each year's mass health screenings.
The year-by-year trends in the values of total cholesterol were such that the period of 18 years witnessed a rise of about 10mg/dl among men and about 6mg/dl among women in the age bracket of 29 and under, about 18-20mg/dl among men and about 16-17mg/dl among women in that of 30-59, and about 10-13mg/dl both among men and women in that of 60 and over. There were signs that the pace of rises from 1991 on was slower than during the 1981-1990 period.