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Changes in methods of reporting blood lipid levels from 1984 to 1987 were studied in 16 medical laboratories in Nebraska. The precision and accuracy of the laboratories was assessed. Fourteen of the 16 laboratories had altered the range of cholesterol values considered normal; 86 percent had lowered what they considered the upper limit of normal values. Eleven out of the 16 laboratories took patient age into account when calculating normal values in 1987, compared with only seven out of 20 in 1984. None of the laboratories took gender into account when calculating normal values in 1984, but five did so in 1987. Similar trends were seen in the reporting of related substances. Reporting procedures varied greatly, and only one laboratory used the risk level standards of the National Cholesterol Educations Program in reporting total blood cholesterol levels. Fifteen of the laboratories met NCEP standards for precision (number of decimal places) and 78 percent met NCEP standards for accuracy (within five percent of true value)., ABSTRACT: The National Cholesterol Education Program has recommended that all laboratories be consistent, precise, and accurate in the reporting and measurement of blood cholesterol levels. In a follow-up to a 1984 survey study, we assessed the changes in reporting procedures for measurements of blood lipid levels in 16 clinical laboratories in Nebraska. Using human serum reference materials of known cholesterol concentrations provided by the Centers for Disease Control, we also assessed the precision and accuracy of measurement of blood cholesterol levels in clinical laboratories in Nebraska. Fourteen of the 16 laboratories restudied in 1987 had altered the reference range for total serum cholesterol since 1984, 86% of whom lowered the upper limit of the reference range. Eleven of 16 laboratories expressed reference ranges for total serum cholesterol in terms of patient age in 1987, while only 7 of 20 did in 1984. Gender-based reference ranges increased from 0 to 5 from 1984 to 1987. Similar trends were seen in the reporting of high-density lipoprotein cholesterol and triglyceride concentrations. Reporting procedures varied greatly; only 1 laboratory used National Cholesterol Education Program risk levels for measuring total serum cholesterol levels. Fifteen laboratories met the National Cholesterol Education Program recommendation for precision (coefficient of variation,