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Direct measurement of cholesterol levels comparable to standard methods

By Jeremy Cockerill | March 12, 2010

Direct measurement of both high- and low-density lipoprotein cholesterol (HDL-C and LDL-C) using modern assay techniques reveals similar levels to those found using standard methods, say US researchers.

In the past, a number of issues have made direct measurement of cholesterol values difficult. For example, HDL-C measurement required a manual precipitation step.

The Friedewald formula has been the standard method used to estimate LDL-C levels. However, now that high-throughput, standardized, automated assays are available, Schaefer and co-workers were able to check how closely cholesterol levels calculated using the new techniques correlated with those using the Friedewald formula and HDL-C following manual precipitation.

Ernst Schaefer (Tufts University, Boston, Massachusetts) and co-workers analysed fasting plasma samples from patients from the Framingham Offspring study. Samples from 1508 men (1335 controls, 173 coronary heart disease [CHD] cases) and 1680 women (1606 controls, 74 CHD cases) were included in the analysis.

The researchers found that values for direct LDL-C and HDL-C correlated well with standard methods. They note that the correlation between calculated and direct values for HDL-C is important since direct HDL-C assays are now very widely used and have not previously been evaluated in large-scale populations studies of CHD risk. However, the calculated and direct measurements differed by more than 10% for 7.7% of samples for LDL-C, and for 8.5% of samples for HDL-C.

Another aim of the study was to assess whether patients with CHD had reached the recommended goals for LDL-C (2.6 mmol/l; 100 mg/dl) set by the Adult Treatment Panel of the National Cholesterol Education Program of the National Institutes of Health. However the values for both men (2.99 mmol/l; 115.7 mg/dl Friedewald/ 3.07 mmol/l; 118.8 mg/dl direct) and women (3.33 mmol/l; 128.9 mg/dl Friedewald/3.46 mmol/l; 133.9 mg/dl direct) were well above this target.

Schaefer and co-workers note that despite four-fold greater use of cholesterol-lowering medication in male and female cases versus controls, less than half of cases were receiving such medication.

“Overall, our data indicate that the direct assays for both LDL-C and HDL-C provide an acceptable guide for lipid treatment, and that in this population there is still substantial residual CHD risk and under-treatment of LDL-C values, with a very high percentage of CHD cases not being at the recommended LDL-C targets, especially in women,” they conclude in the journal Atherosclerosis.